JP7790864B2 - Optical devices, imaging devices - Google Patents

Description

The present invention relates to a photochromic element, and an optical device, imaging device, and lens unit that use the same.

Neutral density (ND) filters, a type of light-adjusting element, reduce the amount of light while minimizing the impact on color and are widely used in still and video photography. In recent years, variable ND filters that can electrically change the ND filter's ND filter attenuation have been put into practical use, enabling previously impossible image expression. These variable ND filters use multiple compounds whose light absorption characteristics change in response to external stimuli (especially electrically), and the combination of the light absorption of these multiple compounds allows for control of ND attenuation while minimizing the impact on color.
One of the important characteristics of an ND filter is that it has a small effect on color reproducibility due to the light source. An ideal ND filter has a constant transmittance regardless of the wavelength of transmitted light (highest wavelength flatness), and such an ND filter can eliminate the effect of the light source on color. Therefore, conventional ND filters have suppressed the effect of the light source on color reproducibility by improving wavelength flatness. Patent Document 1 describes an ND filter that uses a multilayer film with high wavelength flatness and has an invariable attenuation (fixed attenuation). An ND filter with such high wavelength flatness can minimize the effect of the light source on color reproducibility.

Japanese Patent Application Laid-Open No. 2009-175225

In variable ND filters using multiple compounds whose light absorption characteristics change in response to external stimuli, the ND properties may be exhibited by combining the absorption spectra of the multiple compounds. In this case, there is a limit to how much control can be given to the absorption wavelengths of the multiple compounds, making it difficult to achieve a highly flat spectrum like an ND filter whose attenuation does not change (a conventional ND filter with fixed attenuation). The inventors have made repeated efforts to improve wavelength flatness, but it has been difficult to achieve a variable ND filter that highly suppresses the influence of the light source on color reproducibility.
The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a light-adjusting element such as a variable ND filter that highly suppresses the substantial influence of the light source on color reproducibility, and a device that uses the light-adjusting element.

A first aspect of the present invention is an optical device including a photodetector and a photochromic element having a plurality of compounds whose light absorption characteristics change in response to an external stimulus,
the plurality of compounds are compounds having different absorption wavelengths,
the light-adjusting element has a variable transmittance VT(λ) that is a combination of the light absorption characteristics of the plurality of compounds;
the photodetector has a detection light wavelength range of x bar: 580 nm to 680 nm, y bar: 500 nm to 580 nm, and z bar: 425 nm to 500 nm in CIE color matching functions;
The reference illuminant is selected from CIE D65, D55, D50, Illuminant B, and Illuminant C;
When the reference illuminant is CIE A illuminant,
An optical device characterized in that NWD _Max < NWD _MaxFP .
NWD _Max : The maximum value of the ratio of the signal intensity of the transmitted light for each wavelength range of the detection light incident on the photodetector in the transmission state and dimming state of the dimming element, between the reference light source and the reference light source (reference light source/reference light source or reference light source/reference light source). NWD _MaxFP : The NWD _Max at the concentration ratio of the multiple compounds at which the wavelength flatness TF of the VT(λ) in the wavelength range of the detection light is the minimum value TF _FP .
A second aspect of the present invention is an imaging device having an optical system with a plurality of lenses and the optical device of the present invention, characterized in that the imaging element receives light that has passed through the optical system, and the dimming element is arranged between the optical system and the imaging element as an optical filter.

The present invention provides a light-adjusting element such as a variable ND filter that highly suppresses the substantial influence of the light source on color reproducibility, as well as optical devices, imaging devices, and lens units that use the light-adjusting element.

1 is a diagram schematically illustrating an example of an optical device including a light-adjusting element according to the present invention. FIG. 10 is a diagram illustrating an example of the spectral sensitivity of a photodetector. FIG. 2 is a diagram illustrating an example of the spectrum of a light source. 1 shows the spectrum of the change in extinction coefficient of the EC compound used in the examples. 1 shows the variable absorbance spectrum and variable transmittance spectrum of the EC device of Example 1. 1 shows the variable absorbance spectrum and variable transmittance spectrum of the EC element of Comparative Example 1. 1 shows transmission spectra of the EC elements of Example 1 and Comparative Example 1 in a transmitting state and a dimming state. FIG. 1 is a diagram showing the evaluation results of the influence of a light source on the color reproducibility of the EC elements of Example 1 and Comparative Example 1. FIG. 1 is a diagram showing the evaluation results of the influence of a light source on the color reproducibility of the EC elements of Example 1 and Comparative Example 1. 1 shows variable transmittance spectra of the EC elements of Examples 2 and 3. FIG. 10 is a diagram showing the evaluation results of the influence of light sources on the color reproducibility of the EC elements of Examples 2 and 3. 1 shows variable transmittance spectra of the EC elements of Examples 4 and 5 and Comparative Examples 2 and 3. FIG. 10 is a diagram showing the evaluation results of the influence of light sources on the color reproducibility of the EC elements of Examples 4 and 5 and Comparative Examples 2 and 3. FIG. 2 is a diagram illustrating an example of the spectrum of a light source. 10 is a variable transmittance spectrum of the EC element of Example 6. FIG. 10 is a diagram showing the evaluation results of the influence of light sources on the color reproducibility of the EC elements of Example 6 and Comparative Example 3.

The photochromic element of the present invention contains multiple compounds whose light absorption characteristics change in response to external stimuli, and exhibits variable light absorption in the visible light region by superimposing the absorption spectra of the multiple compounds. When the transmission spectrum of the photochromic element is plotted with wavelength on the horizontal axis and transmittance on the vertical axis, the absorption spectrum can be made closer to flat by adjusting the concentration ratio of the multiple compounds. The photochromic element of the present invention is an element that places more importance on suppressing the substantial influence of the light source on color reproducibility than on the flatness of the absorption spectrum, and is evaluated using the parameter NWD _Max .

Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and appropriate modifications and improvements to the following embodiments based on the common knowledge of those skilled in the art are also included within the scope of the present invention, provided they do not deviate from the spirit of the present invention.

<Optical device equipped with a light-adjusting element>
Fig. 1 is a schematic diagram showing an example of an optical device equipped with a photochromic element of the present invention. In Fig. 1, the optical device 1000 has a photochromic element 1001 such as a variable ND filter, and a photodetector 1002 such as an image sensor having a plurality of detection light wavelength regions such as R (red), G (green), and B (blue). Note that if a photodetector is provided separately from the optical device 1000, the optical device 1000 does not need to have the photodetector 1002. Examples of optical devices according to this embodiment include a camera system (including a camera and a lens) with a variable ND filter, a variable transmittance window, variable transmittance glasses, and a variable reflectance mirror.

<Photodetector>
The photochromic element of the present invention is intended for use with a specific photodetector. In other words, the photochromic element of the present invention is designed to function in combination with a specific photodetector. Examples include a combination of an imaging element such as a camera system with a CMOS sensor, a combination of a variable transmittance window with a human eye, a combination of variable transmittance glasses with a human eye, and a combination of a variable reflectance mirror with a human eye. The photodetector has multiple detection wavelength ranges. Specifically, in the case of an imaging CMOS sensor, the detection wavelength ranges are R, G, and B, and in the case of a human eye, the detection wavelength ranges are, for example, the x-bar, y-bar, and z-bar CIE color matching functions. Examples of CIE color matching functions include CIE (1931), CIE (1964), and CIE (2006), and functions for a 2-degree field of view and a 10-degree field of view can be selected. While any value may be used to calculate RRGAC, the 2-degree field of view of CIE (1931) is particularly preferred.

The photochromic element of the present invention can also be used as a component of an optical filter in an imaging device that includes an optical system having multiple lens systems, an optical filter, and an imaging element that receives light that has passed through the optical filter. Furthermore, the photochromic element of the present invention can be combined with an imaging optical system having multiple lenses to form a lens unit. Such a lens unit can be connected to an optical device that includes a photodetector, and by connecting the lens unit to the optical device, the lens unit is positioned so that transmitted light that has passed through the lens unit enters the photodetector. Furthermore, the photodetector has multiple detection light wavelength ranges and may be an imaging element.

<Compounds whose light absorption properties change in response to external stimuli>
The light-adjusting element of the present invention absorbs light by combining multiple compounds whose light-absorption characteristics change in response to external stimuli. Examples of such external stimuli include electrical stimuli, thermal stimuli, optical stimuli, and pH stimuli. Examples of compounds whose light-absorption characteristics change in response to external stimuli include electrochromic (EC) compounds, liquid crystal compounds (including guest-host liquid crystals), thermochromic compounds, photochromic compounds, and pH-responsive compounds. Among these, compounds whose light-absorption characteristics change electrically are preferred from the standpoints of stability, ease of external control, and response speed. Among compounds whose light-absorption characteristics change electrically, electrochromic compounds (EC compounds) and liquid crystal compounds are preferred. In particular, light-adjusting elements using EC compounds are preferred because they can achieve both a high-transmittance light-transmitting state and a low-transmittance dimming state.

When creating a photochromic element using compounds whose light absorption properties change in response to these external stimuli, it is not easy to achieve high color reproducibility by changing the light absorption properties of a single compound alone; it is preferable to utilize the changes in the light absorption properties of multiple compounds. To effectively utilize the changes in the light absorption properties of multiple compounds, it is useful to select compounds with different light absorption wavelengths and combine their strong and weak absorption properties to improve color reproducibility.

The photochromic element of the present invention absorbs light using a combination of multiple compounds whose light absorption characteristics change in response to external stimuli, thereby substantially suppressing the effect of the light source on the color reproducibility of the variable ND filter. The reason for using multiple compounds is that if only one compound is used, the spectral shape that makes up the spectrum of the variable ND filter is determined by that compound, and color reproducibility beyond that of the spectrum of that compound cannot be expected, making it impossible to substantially suppress the effect of the light source on color reproducibility.

The number of compounds to be combined is preferably three or more, for the reasons described below.
(1) When forming a variable transmittance spectrum by combining compounds with different variable absorption spectra, the more types of compounds there are, the more detailed the absorption wavelengths can be complemented. As a result, higher color reproducibility and the substantial light source effect on color reproducibility can be suppressed. Specifically, this can be explained as follows: In terms of concentration ratio, when there are two types of compounds, once the concentration ratio of one compound is determined, there is no flexibility in the concentration ratio of the other two compounds. When there are three or more types of compounds, even if the concentration ratio of one type of compound is determined, there is flexibility in the concentration ratio of the other two compounds, making it possible to complement more detailed absorption wavelengths.

(2) The spectrometer targeted by the ND filter has three or more detection wavelength ranges, as typified by the human eye and RGB sensors. Therefore, if the number of compounds is three or more, the degree of light absorption corresponding to each detection wavelength range can be adjusted relatively freely relative to other compounds, thereby dramatically increasing the effect of optimization using NWD _Max . Specifically, the number of compounds is preferably four or more, and more preferably six or more.

From the above perspective, it is preferable that at least one compound selected from the plurality of compounds has a peak in its variable absorption spectrum in each of the plurality of detection light wavelength ranges of the photodetector. This allows for greater flexibility in setting the optical absorption corresponding to the detection light wavelength range of the photodetector for other compounds. In this case, each of the plurality of detection light wavelength ranges of the photodetector is the wavelength range of the detection wavelength range that is maximum in the normalized sensitivity spectrum of the photodetector. For example, in Figure 2(b), the detection light ranges of the plurality of detection light wavelength ranges (x bar, y bar, z bar) are x bar: 580 nm to 680 nm, y bar: 500 nm to 580 nm, and z bar: 425 nm to 500 nm. It is preferable that at least one compound selected from the plurality of compounds has a peak in its variable absorption spectrum in each of these ranges.

<Principles of improving color reproducibility>
In conventional photochromic devices, the influence of light sources on color reproducibility has been suppressed by improving wavelength flatness. In the photochromic device of the present invention, the substantial influence of light sources on color reproducibility is suppressed by prioritizing reducing the ratio of the detection signal ratio change between the reference light source and the control light source in each of the multiple detection light wavelength ranges of the photodetector, rather than improving wavelength flatness. The principle of improving color reproducibility in the photochromic device of the present invention is described in detail below.

The amount of light that passes through a photochromic element to the image sensor (photodetector) or the human eye is proportional to the photochromic element's transmittance. Therefore, when discussing color reproducibility, transmittance normalized by the amount of light is used. If the spectrum of this normalized transmittance does not change, the influence of the light source on color reproducibility can be eliminated by correction. However, the photochromic element of the present invention is a light-absorbing element, and multiple compounds are combined to form an absorbance (absorption) spectrum with a specific shape. In this case, the shape of the absorbance spectrum is basically (ideally) constant regardless of concentration (in other words, the normalized absorbance spectrum does not fundamentally change). Meanwhile, since the relationship between absorbance Abs and transmittance T is T = 10 ^-Abs , even if the shape of the absorbance spectrum is constant, the spectrum of the normalized transmittance is not constant, and the deviation from the average value increases as absorbance increases. As a result, it becomes difficult to eliminate the influence of the light source on color reproducibility by correction.

Therefore, in this invention, the influence of light sources on color reproducibility is suppressed primarily through the relationship between the photodetector and the light source. Specifically, the relationship between the sensitivity of the photodetector and the intensity of the light source suppresses deviations from the average value of normalized transmittance in wavelength regions with high signal intensity. For example, photodetectors used in image sensors typically have wavelength sensitivity characteristics as described above in the <Photodetector> section, and primary light sources have a fairly continuous intensity spectrum, as described in the light source section (described below). Thus, the sensitivity of the detector and the intensity of the light source each have their own characteristic wavelength dependence. If the transmittance of the photochromic element deviates significantly compared to other wavelength regions in wavelength regions where the signal intensity is high, which is proportional to the product of this sensitivity and intensity, changes in the light source have a significant impact. Conversely, in wavelength regions with low signal intensity, even if the deviation in the transmittance of the photochromic element is large, the impact is relatively small. The photochromic element of this invention utilizes this concept to suppress deviations from the average value of normalized transmittance in wavelength regions with greater impact, thereby substantially suppressing the influence of light sources on color reproducibility.

Here, we will explain the term "substantially." For example, if you are trying to suppress the light source effects of any light source, or in an extreme case, a light source with a uniform wavelength at all wavelengths, such as laser light, you would be improving wavelength flatness. However, the light used in environments where photochromic elements are primarily used is often natural light or light that mimics natural light, and has a fairly continuous spectrum with a wide wavelength distribution. If it is possible to accommodate the light sources used in environments where such photochromic elements are used, then it will be possible to substantially suppress the light source effects.

<Variable transmittance VT (λ)>
The variable transmittance VT(λ) is defined as a combination of the light absorption characteristic changes (e.g., the change in extinction coefficient Δε(λ)) of each of the multiple compounds whose light absorption characteristics are variable, which are included in the photochromic element of the present invention. Here, the change in extinction coefficient Δε(λ) is the change in the molar extinction coefficient obtained by subtracting the molar extinction coefficient of the compound whose light absorption characteristics are variable in the transmitted state from the molar extinction coefficient of the compound whose light absorption characteristics are variable in the dimmed state. Furthermore, the variable transmittance VT(λ) is the change in the transmittance of the photochromic element in the dimmed state divided by the transmittance of the photochromic element in the transmitted state. If the change in extinction coefficient of a compound m whose light absorption characteristics are variable is Δε _m (λ), the concentration in the dimmed state is C _m , and the optical path length of the photochromic element is L, then VT(λ) can be expressed by the following formula: Note that m is 1 or more and is equal to or less than the total number of compounds whose light absorption characteristics are variable used in the photochromic element.

In the above formula,
Δε _m (λ): the change extinction coefficient of compound m (m is 1 to the total number of compounds)
C _m : concentration of compound m in the dimmed state L : optical path length of the dimming element [m]

Examples of the optical path length L and the concentration _Cm in the dimming state are described below. In the case of a transmission-type ND filter, the optical path length L can be the thickness of the layer in which the compound whose light absorption characteristics change is held. Furthermore, when light is reflected from the back surface of the ND filter and travels back and forth within the ND filter, the optical path length L can be twice the thickness of that layer. The concentration _Cm is the average concentration of the compound whose light absorption characteristics change in the dimming state in the thickness of the layer in which the compound whose light absorption characteristics change. Here, being in the dimming state means that the variable state of the compound whose light absorption characteristics change is more prevalent when the photochromic element is in the dimming state than when it is in the transmitting state. Specific examples include EC compounds and dichroic dyes that exhibit changes in light absorption characteristics in the visible light region, and the state in which they exhibit high light absorption in the visible light region.

<Wavelength flatness TF>
The wavelength flatness of VT(λ) in the detection wavelength range of the photodetector is defined as TF. The detection wavelength range of the photodetector refers to the wavelength range in which the photodetector has significant spectral sensitivity. The spectral sensitivity of the photodetector refers to the spectral sensitivity when used in the normal configuration for that photodetector. Specifically, when the photodetector is used as a camera system, this refers to the spectral sensitivity including other optical elements normally used in that camera system, such as UV and IR cut filters and low-pass filters. Figure 2(a) shows an example of the spectral sensitivity of an RGB image sensor when the photodetector is used as a camera system, including the influence of the transmittance of the UV and IR cut filters and low-pass filters. When the photodetector is the human eye, this corresponds to the CIE color matching functions.

Figure 2(b) shows the CIE color matching functions. A typical example of the detection light wavelength range of these photodetectors is the range from 425 nm to 680 nm. Another example is a wavelength range with a sensitivity of 10% or more of the maximum spectral sensitivity of the photodetector. The wavelength flatness TF can be calculated by dividing the difference between the maximum and minimum values of VT(λ) in the detection light wavelength range of the photodetector by the average value, as shown in the following formula.

<Light source>
The light source of light incident on the photochromic element (light that ultimately enters the photodetector through the photochromic element) is described below. The photochromic element of the present invention is a photochromic element that substantially suppresses the influence of the light source on color reproducibility. The light source includes the source of light incident on the photochromic element (light source) itself and light emitted from the light source that has passed through a filter or the like. For example, when using artificial light source lighting, it includes not only the artificial light source but also the filter or the like when the artificial light source is used for lighting or the like with a filter or the like attached. For example, when considering sunlight on Earth, it includes sunlight that has passed through the Earth's atmosphere and reached the Earth's surface. Light sources can be classified by color temperature into three types: low color temperatures of 4000 K or less, medium color temperatures of 4000 K to 7000 K, and high color temperatures of 7000 K or higher.

The photochromic element of the present invention suppresses the substantial light source impact on color reproducibility by prioritizing reducing the ratio between the reference light source and the control light source in the change in the detection signal ratio in each of the multiple detection light wavelength ranges of the photodetector. There are two methods for selecting the reference light source and the control light source. For ease of understanding, we will use an example in which the photochromic element is used as an optical filter in an imaging device. One method involves leaving the settings (corrections) of the imaging device unchanged depending on the light source, while the other involves changing the settings (corrections) of the imaging device depending on the light source. Each method is described below.

In the former case, natural daylight, which is frequently used with dimming elements, is preferably selected as the reference light source, and a light source with a corresponding medium color temperature is preferably selected. Figure 3(a) shows examples of the spectrum of natural daylight and a simulated solar light source with a color temperature of approximately 5000 K. Examples of defined light sources include CIE D65, D55, D50, illuminant B, and illuminant C.

Selecting a reference light source for the reference light source that is important (used relatively frequently) in the environment in which the photochromic element will be used makes it possible to highly demonstrate the ND properties of the photochromic element. An example of the color temperature of the reference light source is a color temperature of 2000K to 9000K. Figure 3(b) shows examples of light sources corresponding to each color temperature, including the spectra of light sources with color temperatures of 3200K, 5600K, and 8000K. Light sources with low color temperatures are important as traditionally commonly used artificial light, such as sunlight at low altitudes, incandescent lamps, and halogen lamps. Light sources with medium color temperatures are important as artificial light that simulates natural daylight as a reference light source. Light sources with high color temperatures are important, for example, when trying to express colors in the shade. In particular, light sources with color temperatures of 2000K to 4000K or 7000K to 9000K are important as reference light sources, from the perspective of compatibility with a reference light source with a medium color temperature.

In addition to compatibility with the above-mentioned standard light sources, light sources with a color temperature of 2000K to 4000K are important as commonly used artificial light. Specific light sources include those listed in the low color temperature light sources section above, and an example of a defined light source is the CIE A illuminant.

The photochromic element of the present invention is preferably compatible with light sources of multiple color temperatures. It is even more preferable that it be compatible with multiple color temperatures, including a medium color temperature. For example, it is preferable that it be compatible with medium and low color temperatures, medium and high color temperatures, and medium, low, and high color temperatures. Here, compatibility with a light source of a certain color temperature means that NWD _Max < NWD _MaxFP can be achieved even when that light source is used. Being compatible with light sources of multiple color temperatures can expand the range of application of photochromic elements. Specifically, photochromic elements can exhibit high color reproducibility regardless of the color temperature of the light source. For example, a camera can exhibit high color reproducibility without having to distinguish the color temperature of the light source.

An example of the latter (changing the imaging device settings (corrections) depending on the light source) is estimating the color temperature of the light source and changing the imaging device settings (correction values) for each color temperature. An example of this correction value is the white balance correction value. In this case, changes in the correction value based on the light source color temperature are compensated for by correction based on the estimated color temperature of the light source. Therefore, while it is possible to accommodate light sources with multiple color temperatures, it is preferable to first accommodate multiple light sources within a single color temperature range. Specifically, this would involve a combination of a reference light source with a medium color temperature and a control light source with a medium color temperature. Generally, when different light sources selected from the same color temperature range are used, the light source's influence on color reproducibility is often smaller than when light sources selected from different color temperature ranges are used, but exceptions do occur frequently. When different light sources selected from the same color temperature range are used, the most common issue regarding the influence of light sources on color reproducibility is the influence of light sources with spectra with large intensity fluctuations. Specific examples include fluorescent lamps and LED light sources. Figure 14 shows an example of the spectrum of a daylight fluorescent lamp (color temperature 5000 K). This shows that there are large changes in spectral intensity. Fluorescent lamps, in particular, are greatly affected by emission lines, making the influence of the light source on color reproducibility a common issue. When using such light sources, it is preferable to select a reference light source and a control light source by selecting a light source with a continuous spectrum as the reference light source and a light source with a spectrum with large intensity fluctuations as the control light source. Light sources with a continuous spectrum include natural daylight, simulated sunlight, D65, D55, D50, B light source, and C light source as light sources with medium color temperatures. Furthermore, halogen lamps and A light source are examples of light sources with low color temperatures.

Furthermore, to improve the color reproducibility of a photochromic element, it is desirable to faithfully reproduce a variety of colors. Therefore, it is preferable to imagine the light incident on the photochromic element as light from the above-mentioned light source reflected by samples of various colors. A specific example of a color sample is a color checker (e.g., an x-rite Color Checker).

<NWD _Max >
In the photochromic element of the present invention, the substantial influence of the light source on color reproducibility is suppressed by prioritizing the reduction of the ratio of the change in the detection signal ratio between the reference light source and the control light source in each of the multiple detection light wavelength ranges of the photodetector, rather than improving wavelength flatness. The parameter NWD _Max for achieving this will be explained using the schematic diagram of the optical device in Figure 1.

The variable transmittance of the dimming element 1001 is VT(λ), the transmission spectrum in the transmitted state is _T0 (λ), and the spectral sensitivities of the photodetector (RGB image sensor) 1002 are D _R (λ), D _G (λ), and D _B (λ) for R, G, and B, respectively. When incident light 1003 having a spectrum of I _n (λ) is incident on this optical device 1000 and passes through the dimming element 1001, the signal intensities obtained from the photodetector 1002 are S _Rn , S _Gn , and S _Bn , respectively. Here, n = 0 means the reference light source ( _I0 ), and n = 1 means the control light source ( _I1 ). At this time, the signal intensities S _RTn (S _RT0 or S _RT1 ), S _GTn (S _GT0 or S _GT1 ), and S _BTn (S _BT0 or S _BT1 ) in the transmitted state are described by the following equations:

In the above formula,
λ ₀ : Lower limit wavelength of the detection light wavelength range of the photodetector λ ₁ : Upper limit wavelength of the detection light wavelength range of the photodetector

Similarly, the signal intensities _SRCn (SRC0 or SRC1), _SGCn ( _SGC0 or _SGC1 ), and SBCn ( _SBC0 or _SBC1 ) of the dimming element (where the variable transmittance from the transmitting _state is _VT ( _λ )) are described by the following equations:

The transmittance of a dimming element in the dimming state functions as the transmittance multiplied by the variable transmittance VT (λ). A dimming element in this transmissive state has higher transmittance than a dimming element in the dimming state. This is typically the dimming element's highest transmittance state. If the spectrum of the dimming element in the highest transmittance state provides poor color reproduction, it is preferable to select a transmissive state within the range in which the dimming element can be effectively used. The dimming ratio between the transmissive and dimming states of this dimming element (the ratio of the amount of light emitted when the same amount of light is incident (transmissive state/dimming state)) is preferably 8 (ND8) or greater, and more preferably 32 (ND32) or greater. There are two reasons for this:

(1) Usefulness as a dimming element: When the dimming ratio is 8 or less, the adjustable range of the dimming element is limited, and the range of application as a dimming element is severely limited. On the other hand, when the dimming ratio is 32 or more, the applicability as a dimming element is dramatically expanded.

(2) The greater the dimming ratio, the more difficult it becomes to achieve high color reproducibility.
A photochromic element that absorbs light by combining multiple compounds with variable light absorption characteristics is a light-absorbing element, and by combining multiple compounds, it forms an absorbance (absorption) spectrum with a specific shape. The shape of this absorbance spectrum is essentially (ideally) constant regardless of concentration. Meanwhile, the amount of light entering the image sensor (a photodetector) or the human eye is determined by the ratio of incident light amount x transmittance. Therefore, when discussing color reproducibility normalized by light amount, normalized transmittance is used. Here, the relationship between absorbance Abs and transmittance T is T = 10 ^-Abs , so the influence of wavelength-dependent variations in absorbance increases exponentially with increasing absorbance. Therefore, when the extinction ratio is small, at 8 or less, the impact of changes in the extinction ratio of the photochromic element on color reproducibility is relatively small. On the other hand, when the extinction ratio is 8 or more, the impact of changes in the extinction ratio of the photochromic element on color reproducibility becomes significant, and when the extinction ratio is 32 or more, the impact becomes extremely large. By using the photochromic element technique of the present invention, high color reproducibility can be achieved even in such a large extinction ratio range.

At this time, the signal intensity ratio W _RTn (W _RT0 or W _RT1 ) and W _BTn (W _BT0 or W _BT1 ) of the R and B detection wavelength ranges of the photodetector in the transmitted state, with G as the reference, is described as the gain (reciprocal) with G as the reference, as shown in the following equation.
W _RTn = S _GTn / S _RTn
WBTn = _SGTn / _SBTn

Similarly, the signal intensity ratio _WRCn ( _WRC0 or _WRC1 ) and _WBCn ( _WBC0 or _WBC1 ) of the R and B detected light wavelength regions of a photodetector in a dimmed state, with G as the reference, are expressed as gains (reciprocals) with G as the reference, as shown in the following equation:
_WRCn = _SGCn / _SRCn
WBCn = _SGCn / _SBCn

NW _Rn (NW _R0 or NW _R1 ) and NW _Bn (NW _B0 or NW _B1 ) used as the degree of change in the detection signal ratio are described by the change between the signal intensity ratio in the transmitted state and the signal intensity ratio in the dimmed state (dimmed state/transmitted state) as shown in the following equation:
NW _Rn =W _RCn /W _RTn
NW _Bn =W _BCn /W _BTn

The ratio NWD _Max of the detection signal ratio change between the reference light source and the control light source is the largest of the ratios between the reference light source and the control light source for each of NW _Rn and NW _Bn (reference light source/control light source or control light source/reference light source). In other words, NWD _Max is the largest value among the following four ratios:
NW _R1 / NW _R0
NW _R0 / NW _R1
NW _B1 / NW _B0
NW _B0 / NW _B1

The minimum value of the wavelength flatness of the transmission spectrum obtained by combining the optical absorption characteristic change spectra of multiple compounds is defined as TF _FP , and the NWD _Max at this point is defined as NWD _MaxFP . This minimum value TF _FP and the variable transmittance VT _FP (λ) that gives TF _FP can be calculated by performing a minimization calculation using the optical absorption characteristic change spectra of multiple compounds. NWD _MaxFP is then calculated using VT _FP (λ) and the above formula.

In the photochromic element of the present invention, priority is given to reducing the ratio of the change in the detection signal ratio between the reference light source and the control light source in each of the multiple detection light wavelength ranges of the photodetector rather than improving the wavelength flatness, so that the wavelength flatness TF of the photochromic element of the present invention satisfies TF > TF _FP and NWD _Max < NWD _MaxFP .

A preferred value of NWD _Max will be described. Because the value of NWD _Max changes depending on the amount of change in the variable transmittance VT(λ), it is preferable to evaluate it using a normalized value. Therefore, it is evaluated using a value normalized so that the average change in the variable transmittance VT(λ) in multiple detection light wavelength regions of the photodetector is 1/64 (ND64). Because the shape of the variable transmittance spectrum changes with changes in transmittance, normalization is performed by converting the variable transmittance spectrum to a variable absorbance spectrum (given by -log(VT(λ))), and then normalizing it back to the variable transmittance spectrum. When simulated images passed through a group of filters with different NWD _Max values in a dimming state were sensorily evaluated, the range of NWD _Max in which the image was perceived as natural was 1.03 or less, compared to images passed through the same filters in a transmitting state. Therefore, a preferred NWD _Max value is 1.03 or less when using a variable transmittance VT(λ) normalized so that the average change is ND64.

<Electrochromic element (EC element)>
The photochromic element of the present invention absorbs light by combining multiple compounds whose light absorption properties change in response to an external stimulus. EC elements using EC compounds are most preferably used because they can achieve both a high light transmission state and a low light transmission state. Photochromic elements using EC elements are described in detail below.

EC elements are available in two types: those made with inorganic materials and those made with organic materials; an example of the former is one made with tungsten oxide. EC elements made with organic materials include polymer-type and low-molecular-weight EC elements; an example of the former is one made with polythiophene. In order to create a light-controlling element with high color reproducibility, it is necessary to precisely control the light absorption characteristics, and from this perspective, low-molecular-weight EC elements are preferred. Specifically, it is preferable to select low-molecular-weight EC compounds with different light absorption wavelengths and combine their strong and weak absorption points to improve color reproducibility.

A typical EC element is constructed by placing two transparent conductive electrodes, at least one of which is transparent, facing each other, placing an EC layer containing an EC compound in the space between them, and sealing the periphery with a sealant. By controlling the voltage between these electrodes, the EC element can be changed from a transmissive state to a dimming state.

<Electrode>
The electrodes are preferably made of a material that can stably exist in the operating environment of the EC device and rapidly undergo a redox reaction in response to the application of an external voltage. Examples of materials that can be used for the electrodes include transparent conductive materials such as tin-doped indium oxide (ITO) and fluorine-doped tin oxide (FTO), as well as metals. By using a transparent electrode for at least one of the electrodes, light can be efficiently taken in from outside the EC device, allowing it to interact with the EC compound in the EC layer, thereby allowing the optical properties of the EC compound to be reflected in the emitted light.

<Sealing material>
The sealing material is preferably composed of a material that is chemically stable, impermeable to gases and liquids, and does not inhibit the redox reaction of the EC compound. For example, inorganic materials such as glass frit, organic materials such as epoxy and acrylic resins, and metals can be used. The sealing material may also contain a spacer material to maintain the distance between the two electrodes. This allows the distance between the electrodes to be determined, thereby defining the optical path length. The spacer material can be inorganic materials such as silica beads and glass fiber, or organic materials such as polyimide, polytetrafluoroethylene, polydivinylbenzene, fluororubber, and epoxy resin.

<Electrochromic Layer (EC Layer)>
EC elements include unipolar EC elements in which an electrochemical reaction proceeds at one electrode, and complementary EC elements in which an electrochemical reaction proceeds at both electrodes. While either type of EC element can be used as the photochromic element of the present invention, complementary EC elements are preferred in order to increase the extinction ratio between the transmissive and dimmed states of the photochromic element. A typical complementary EC element contains an anodic EC compound that changes from the transmissive state to the dimmed state through an oxidation reaction, and a cathodic EC compound that changes from the transmissive state to the dimmed state through a reduction reaction. Among typical complementary EC elements, EC elements that highly suppress electrochemical reactions other than the electrochemical reaction of the EC compound exhibit minimal color change in the dimmed state even after repeated operation, making them a preferred form of photochromic element of the present invention.

In a complementary EC element that highly suppresses electrochemical reactions other than those of the EC compound, the charge used when the reaction of the anodic EC compound progresses is approximately equal to the charge used when the reaction of the cathodic EC compound progresses. Therefore, in such a complementary EC element, when configuring a variable transmittance VT(λ) that combines changes in the light absorption characteristics of multiple compounds, it is necessary to distinguish between changes in the light absorption characteristics of the anodic EC compound and changes in the light absorption characteristics of the cathodic EC compound. Specifically, the element is configured so that the total charge concentration of the anodic EC compound in the dimmed state is approximately equal to the total charge concentration of the cathodic EC compound in the dimmed state.

Here, the charge concentration in the dimmed state refers to the charge required to produce a concentration of EC compound in the dimmed state, and can be expressed as n x c, where n is the number of reaction electrons used in the reaction that changes the EC material from a transparent state to a dimmed state, and c is the concentration of the EC compound in the dimmed state. Furthermore, "the total charge concentrations are approximately equal" means that the difference in the total charge concentrations is within 10%, preferably within 5%.

As described above, in a complementary EC device, when configuring a variable transmittance spectrum, there are limitations on the sum of the charge concentrations of the anodic EC compounds in the dimmed state and the charge concentration of the cathodic EC compounds in the dimmed state. As described above, the plurality of compounds is preferably three or more compounds. In a complementary EC device, to ensure the degree of freedom in configuring a variable transmittance spectrum under these charge concentration limitations, it is preferable to further include a plurality of both anodic EC compounds and cathodic EC compounds. This is because, even if the above-mentioned charge concentration limitations are present, the dimmed state concentration ratios between anodic EC compounds and between cathodic EC compounds can be freely set. This dramatically increases the optimization effect of the NWD _Max of the present invention.

The EC compound in the EC element may be dissolved in a solvent or the like to form an EC layer, or may be immobilized on an electrode. If immobilized on an electrode, the extinction ratio between the transmitting state and the dimming state can be increased by using a porous electrode to increase the concentration of the adsorbed EC compound. In this case, the thickness of the EC layer is the range in which the EC compound exists where the transmittance changes, and the concentration is the average concentration throughout the thickness of the EC layer.

EC compounds are compounds whose light absorption characteristics change repeatedly in the target light wavelength range of the EC element due to an oxidation-reduction reaction. Some EC compounds have a relatively small change in extinction coefficient. Even compounds with a relatively small change in extinction coefficient change their light absorption characteristics, albeit small, and contribute to the reaction charge. Therefore, when calculating the charge concentration described above, compounds with a small change in extinction coefficient are included as EC compounds.

Examples of anodic EC compounds include thiophene derivatives, amines having aromatic rings (e.g., phenazine derivatives, triallylamine derivatives), pyrrole derivatives, thiazine derivatives, triallylmethane derivatives, bisphenylmethane derivatives, xanthene derivatives, fluoran derivatives, and spiropyran derivatives. Among these, low-molecular-weight amines having aromatic rings are preferred as anodic EC compounds, with dihydrophenazine derivatives being the most preferred. This is because using these compounds as EC compounds facilitates the production of EC devices with desired absorption spectra and provides high durability for repeated use. In their neutral state (reduced form), these compounds have an absorption peak in the ultraviolet region, no absorption in the visible region, and a transparent state with high transmittance in the visible region. When these molecules undergo an oxidation reaction to become radical cations (oxidized forms), the absorption peak shifts to the visible region, resulting in a dimming state. The absorption wavelength of these molecules can be freely designed by adjusting their π-conjugation length and by changing the substituents to modify the π-conjugated system. Here, low molecular weight refers to a molecular weight of 2000 or less.

Cathodic EC compounds are not particularly limited, but examples include pyridine derivatives and quinone compounds. Of these, pyridine derivatives, particularly viologen derivatives, are most preferred. These compounds typically have an absorption peak in the ultraviolet region in their divalent cationic state (oxidized form), no absorption in the visible light region, and a transparent state with high transmittance in the visible light region. When these molecules become radical cations (reduced forms) through a reduction reaction, the absorption peak shifts to the visible light region, resulting in a dimmed state. The absorption wavelength of these molecules can also be freely designed by expanding or contracting their π-conjugation length or by changing the substituents to modify the π-conjugated system. Here, "small molecules" refers to molecules with a molecular weight of 2000 or less, excluding counterions.

<Color reproducibility evaluation method>
The method for evaluating the color reproducibility of the photochromic element of the present invention is described below. It is desirable that the color change of the photochromic element of the present invention when the dimming level is changed does not vary depending on the light source. Therefore, the color of the light incident on the photodetector is evaluated by comparing the change (ratio) between the transmission state and the dimming state of the photochromic element with a reference light source. Specifically, since the brightness changes when the dimming level of the photochromic element is changed, the brightness in the transmission state and the dimming state of the photochromic element are made uniform, and the color difference is plotted on the a ^* b ^* plane in the L ^* a ^* b ^* color space for evaluation. Furthermore, the evaluation is numerically performed using color difference (CIEDE 2000 (ΔE ₀₀ )).

The smaller the color difference, the higher the color reproducibility. The following table, published by Nippon Denshoku Industries Co., Ltd., is a widely known indicator of this.
Class C tolerance (ΔE ₀₀ : 6.5 to 13.0): color difference equivalent to one degree on a JIS standard color chart, Munsell color chart, or the like.
Class B tolerance (ΔE ₀₀ : 3.2 to 6.5): A color difference within the range that can be treated as the same color at the impression level, but which may result in complaints in the paint and plastics industries.
Class A tolerance (ΔE ₀₀ : 1.6 to 3.2) This is a color difference level that is barely noticeable when comparing colors closely, and is generally considered to be the same color.
AA tolerance (ΔE ₀₀ : 0.8 to 1.6): A level where slight color difference can be perceived when comparing adjacent colors. This is the range of allowable color difference that includes errors of general color measurement institutions.

Effect
The photochromic element of the present invention can suppress the substantial influence of light sources on color reproducibility even in an optical device equipped with a photochromic element using multiple compounds, such as multiple compounds whose light absorption characteristics change in response to external stimuli. The present invention prioritizes reducing the ratio of detection signal ratio changes between a reference light source and a control light source in each of multiple detection light wavelength ranges of a photodetector over improving wavelength flatness. This allows the substantial influence of light sources on color reproducibility to be further suppressed than when wavelength flatness is improved.

Specific examples of optical devices that can be realized include camera systems that use variable ND filters to adjust the amount of light, and that exhibit high color reproducibility under a variety of lighting conditions. Other examples include variable transmittance windows and variable transmittance glasses (sunglasses) that display natural colors under a variety of lighting conditions. Furthermore, examples include variable transmittance mirrors (anti-glare mirrors) that display natural colors under a variety of lighting conditions.

The following describes the light-adjusting element of the present invention using examples. Note that all of the following examples are reference examples. Specifically, the following describes an EC element equipped with a variable ND filter using a complementary EC element that absorbs light by combining multiple EC materials whose light absorption characteristics are electrically changed. However, the present invention is not limited to these examples.

[EC compound]
<Anodic EC Compound>
The anodic EC compounds used in this example are listed below, but the EC compounds used in the present invention are not limited to these.

The above EC compounds (1) to (5) can be synthesized using the reaction shown in formula (A) below.

In the above formula (A), _R1 is a hydrogen atom, an alkyl group, or a phenoxy group, and _R2 is a hydrogen atom, an alkyl group, or an aryl group. EC compounds (1) to (5) can be synthesized by performing reduction and isopropylation of the phenazine ring.

For the EC compounds (2) to (4), a _precursor can be synthesized prior to the reaction of formula (A) above by a known Pd-catalyzed coupling reaction using a combination of a halogenated substituted phenazine (X is a halogen) represented by formula (B) below and a phenylboronic acid or boronic acid ester compound having a substituted alkyl group or alkoxy group at the ortho-position (R3, _R4 ). The _R1 position can also be subjected to the same reaction as the _R2 position.

For EC compound (3), a phenoxy group is introduced at the 7-position of the phenazine ring prior to the reactions of formulas (A) and (B) above. The phenoxy group can be introduced by a known Cu-catalyzed coupling reaction using phenol with a halogenated phenazine. The synthesis scheme for EC compound (3), including specific examples of the reactions of formulas (A) and (B), is shown in formula (C) below.

EC compound (3) can be synthesized, for example, by the following procedure. First, the first-stage intermediate was synthesized. 2,7-Dibromophenazine and phenol were mixed in DMSO (dimethyl sulfoxide), and dissolved oxygen was removed with nitrogen. Next, CuI/Spartein complex and potassium carbonate were added, and the mixture was refluxed for 8 hours. The reaction solution was concentrated under reduced pressure and purified by silica gel chromatography to obtain the first-stage intermediate as a yellow solid.

Next, the first-stage intermediate, 2-isopropoxy-6-methoxyphenylboronic acid, was mixed in a toluene/1,4-dioxane mixed solvent, and dissolved oxygen was removed with nitrogen. Pd(OAc)2, 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (S-Phos), and tripotassium phosphate were added, and the mixture was refluxed for 15 hours. The reaction solution was concentrated under reduced pressure and separated and purified by silica gel chromatography to obtain the second-stage intermediate as a yellow solid.

Next, the second-stage intermediate, 2-iodopropane, was mixed in an acetonitrile/water mixed solvent, and dissolved oxygen was removed with nitrogen. Sodium hydrosulfite and potassium carbonate were added, and the mixture was refluxed for 10 hours. The reaction solution was concentrated under reduced pressure and separated and purified by silica gel chromatography to obtain a solid EC compound (3).
¹ H-NMR (heavy acetone) δ (ppm): 7.35 (m, 2H), 7.19 (t, 1H), 7.06 (t, 1H), 6.99 (d, 2H), 6.8-6.65 (m, 6H), 6.49 (d, 1H), 6.4 2 (dd, 1H), 4.47 (sep, 1H), 4.17 (sep, 1H), 3.97 (sep, 1H), 3.71 (s, 3H), 1.51 (d, 6H), 1.46 (d, 6H), 1.18 (d, 6H).

<Cathodic EC Compound>
The cathodic EC compounds used in this example are shown below, but the EC compounds used in the present invention are not limited to these.

The above EC compounds (6) to (8) can be synthesized using the reaction shown in formula (D) below.

In the above formula (D), _R4 is a hydrogen atom or a methyl group, and _R5 is a hydrogen atom or an alkyl group. As an example, a specific synthesis method for the EC compound (7) will be described.

In the first step, 3-methyl-4-chloropyridine hydrochloride, 4-pyridylboronic acid, tris(dibenzylideneacetone)dipalladium(0), tricyclohexylphosphine, and tripotassium phosphate were placed in a reaction vessel and heated under reflux for 8 hours in a dioxane/water solvent under a nitrogen stream. After concentrating the reaction mixture, it was extracted with ethyl acetate, purified by silica gel column chromatography, and recrystallized to obtain 3-methyl-4,4'-bipyridine.

In the second step, 3-methyl-4,4'-bipyridine and 2,4-dinitrobromobenzene were reacted in N,N-dimethylformamide solvent at 100°C for 24 hours, and the precipitated crystals were filtered and washed with acetonitrile to obtain Intermediate 1.

In the third step, intermediate 1, o-toluidine, was refluxed in ethanol for 8 hours. After removing the solvent, ethyl acetate was added and the precipitate was filtered. The resulting crystals were dissolved in water, and an aqueous solution of lithium bis(trifluoromethanesulfonyl)imide was added dropwise. The mixture was stirred at room temperature for 3 hours, and then isopropyl alcohol was added to recrystallize the mixture to obtain EC compound (7).
¹ H-NMR (CD3CN) σ (ppm): 9.00 (d, 2H), 8.89 (s, 1H), 8.83 (d, 1H), 8.33 (d, 2H), 8.12 (d , 1H), 7.76-7.66 (m, 2H), 7.64-7.51 (m, 6H), 2.57 (s, 3H), 2.27 (s, 3H), 2.25 (s, 3H).

The above EC compounds (9) and (10) can be synthesized using the reaction shown in formula (E) below.

In the above formula (E), R ₆ and R ₇ are hydrogen atoms or alkyl groups (forming a ring through R ₆ and R ₇ ). As an example, a specific synthesis method for EC compound (9) is described in formula (F).

First, we will describe the synthesis of the intermediate 9,9-dimethyl-2,7-diazafluorene. The synthesis was carried out with reference to technical literature (E. Botana, et al., Angew. Chem. Int. Ed. 46, 198-201 (2007)). 3,8-phenanthroline, potassium hydroxide, and water were added to a reaction vessel and heated to 90°C. A solution of water and potassium permanganate mixed and heated to 90°C was then added dropwise to the reaction solution. After reacting for one hour, the precipitated solid was filtered, extracted with chloroform, washed with water and saturated brine, dried, and concentrated to obtain a brown powder. This was then separated and purified by silica gel chromatography to obtain the first intermediate, a yellow solid.

The first intermediate, diethylene glycol, and hydrazine monohydrate were added to a reaction vessel and reacted at 100°C for 12 hours. Water was added to the resulting black-red suspension, which was then extracted with dichloromethane, washed with water and saturated brine, dried, and concentrated to yield a black-yellow solid. This was then separated and purified using silica gel chromatography to yield the second intermediate, a yellow-brown solid.

The second intermediate, DMF (dimethylformamide), was added to the reaction vessel and cooled in an ice bath. Potassium tert-butoxide was then added and stirred at the same temperature for 30 minutes, after which iodomethane diluted in DMF was added dropwise. After stirring at the same temperature for another 30 minutes, the reaction was allowed to proceed at room temperature for 3 hours. The resulting reddish-brown suspension was added to saturated aqueous sodium bicarbonate, extracted with ethyl acetate, washed with water and saturated brine, dried, and concentrated to yield a black-yellow solid. This was then separated and purified by silica gel chromatography to yield 9,9-dimethyl-2,7-diazafluorene as a beige solid.

9,9-Dimethyl-2,7-diazafluorene and an excess amount of 1-bromoheptane were added to a reaction vessel, and the mixture was allowed to react at 110°C for 19 hours using DMF as the solvent. The precipitate was collected and dissolved in water, and an excess of lithium bis(trifluoromethanesulfonyl)imide was added. The precipitate was collected by filtration and dried to obtain EC compound (9).

[Fabrication of EC Device]
Two sheets of transparent conductive glass coated with indium-doped tin oxide (ITO) films were prepared and placed so that the ITO films faced each other. The two sheets of transparent conductive glass were then bonded together at their outer peripheries using a sealant containing spacer beads with a particle size of 50 μm. A solution containing a specific EC compound was injected through a pre-formed injection port in the transparent conductive glass, filling the space formed by the two sheets of transparent conductive glass and the sealant with the solution. The injection port was then sealed with a sealant to obtain an EC device.

[Change in extinction coefficient Δε(λ) of EC compound]
The absorbance change spectrum (absorbance in the dimmed state minus absorbance in the transmitted state) of a single EC compound was obtained. Specifically, the EC compound was dissolved at a concentration of 1 mmol/L in a 0.1 mol/L propylene carbonate solution of tetrabutylammonium hexafluorophosphate. A platinum mesh electrode was used as the working electrode, a platinum wire electrode as the counter electrode, and an Ag/Ag ⁺ electrode as the reference electrode. A potential was applied for 120 seconds to induce a dimmed state in a cuvette with a 1 mm optical path length, and the absorbance change spectrum was obtained.

Next, one anodic EC compound and one cathodic EC compound were each dissolved in propylene carbonate at a concentration of 0.05 mol/L, and this solution was used to fabricate an EC device. In a complementary EC device in which electrochemical reactions other than those of the EC compounds are highly suppressed, the amount of charge used to create the dimmed state for the anodic EC compound and the cathodic EC compound is equal. Taking advantage of this, the extinction coefficient change of the reference compound was used to determine the extinction coefficient change of the EC compound with the opposite polarity. Here, 5,10-diisopropyl-5,10-dihydrophenazine (Δε (480 nm) = 6.5 × 10 ³ mol ^-1 Lcm ^-1 ) was used as the reference compound.

Figure 4(a) shows the spectra of the change in extinction coefficient Δε(λ) for EC compounds (1) to (5), and Figure 4(b) shows the spectra of the change in extinction coefficient Δε(λ) for EC compounds (6) to (10). Note that in this example, because the EC element is a complementary type, the change in extinction coefficient Δε(λ) is determined before the variable transmittance VT(λ), but it is also possible to calculate the variable transmittance VT(λ) and its wavelength flatness TF directly from the change in absorbance (without determining Δε(λ)).

(Example 1, Comparative Example 1)
An EC device with variable transmittance VT(λ) was constructed using anodic EC compounds (1), (2), and (3) and cathodic EC compounds (6), (7), and (9) having the Δε(λ) spectrum shown in Figure 4. The wavelength range of the light detected by the photodetector was the 425 nm to 680 nm range of the photodetector shown in Figure 2(a). Here, EC compounds (6), (7), and (9) have variable absorption spectrum peaks in the R region of the photodetector, EC compounds (2) and (3) have variable absorption spectrum peaks in the G region of the photodetector, and EC compounds (1) and (6) have variable absorption spectrum peaks in the B region of the photodetector. The extinction ratio between the transmission state and the extinction state of this EC device was 64 (= average variable transmittance of 1.56%).

Figure 5 shows spectra obtained by combining the Δε(λ) of multiple EC compounds (1), (2), (3), (6), (7), and (9) to reduce NWD _Max for the various light sources shown in Figure 3. An EC device having this EC compound composition is designated Example 1, and the concentrations (units: mmol/L) of each EC compound in the dimmed state and the sum of the charge concentrations of the anodic EC compound and the cathodic EC compound are shown in Table 1. Figure 6 also shows spectra obtained by combining the same EC compounds as in Example 1 to minimize the wavelength flatness of the variable transmittance. An EC device having an EC compound with this composition is designated Comparative Example 1, and the concentrations (units: mmol/L) of each EC compound in the dimmed state and the sum of the charge concentrations of the anodic EC compound and the cathodic EC compound are shown in Table 1.

Table 1 confirms that the total charge concentration in the dimmed state of the anodic EC compound and the total charge concentration in the dimmed state of the cathodic EC compound are approximately equal, at 68.5 mmol/L in Example 1 and 66.2 mmol/L and 66.3 mmol/L in Comparative Example 1.

Fig. 5(a) shows the variable absorbance spectrum VA(λ) of the EC element of Example 1, and Fig. 5(b) shows the variable transmittance VT(λ) obtained by converting VA(λ) of the EC element of Example 1 into transmittance. Fig. 6(a) shows the variable absorbance spectrum VA(λ) of the EC element of Comparative Example 1, and Fig. 6(b) shows the variable transmittance VT _FP (λ) obtained by converting VA(λ) of the EC element of Comparative Example 1 into transmittance.

The wavelength flatness TF in the detection light wavelength region was 103% for Example 1 and 67.6% for Comparative Example 1, and the wavelength flatness TF of Comparative Example 1 was the lowest wavelength flatness TF _FP among the combinations of EC compounds used.

Table 2 also shows the NWD Max values calculated using the spectrum of natural daylight in the daytime shown in FIG. 3(a) as the reference light _source and using light source A, a halogen lamp, and five types of color temperature spectrum shown in FIG. 3(b) ranging from low to high color temperatures as control light sources.

From the comparison in Table 2, it can be confirmed that the EC element of Example 1 is more capable of handling medium, low, and high color temperatures than the EC element of Comparative Example 1.

Fig. 7(a) shows the transmission spectrum of the EC element in the transmitted state (ND0) and the dimmed state (ND64) of Example 1, and Fig. 7(b) shows the transmission spectrum of the EC element in the comparative example 1. Fig. 8(a) shows the results of evaluating the influence of the light source on color reproducibility under the following conditions for the EC element in Example 1, and Fig. 8(b) shows the results of evaluating the influence of the light source on color reproducibility for the EC element in the comparative example 1, under the following conditions.
Transmission spectrum: Figure 7(a) and Figure 7(b)
Spectral sensitivity: Figure 2(a)
Reference light source: Daytime natural light spectrum shown in Figure 3(a) Control light source: Light source A, halogen lamp, color temperature spectrum shown in Figure 3(b)

The evaluation was performed by first obtaining the white balance change (multiple) when the EC element was changed from a transmissive state to a dimmed state using the light source light of a reference light source (subject reflectance = 1), and then calculating a correction value to compensate for this (reduce the change to zero). Next, white balance was performed with the EC element in a transmissive state (ND0) using the light source light of a control light source (subject reflectance = 1), and the correction value of the reference light source obtained earlier was applied. The color of the dimmed state of the EC element, with the luminance normalized at this time, was plotted on the a ^* b ^* plane in the L ^* a ^* b ^* space. In this figure, the closer the dimmed state plot is to the origin (the transmissive state of the EC element after white balancing), the higher the color reproducibility. In other words, the influence of the light source on color reproducibility is small. This means that even when a different light source is used and the dimming level changes, the white image of the subject will still appear white.

8(a) and 8(b), the plot of the dimming state in Example 1, which prioritizes NWD _Max , is closer to the origin (transmitting state) than in Comparative Example 1, which prioritizes wavelength flatness. This shows that the EC element of Example 1, which prioritizes NWD _Max , is able to reduce the influence of the light source on color reproducibility more than the EC element of Comparative Example 1, which prioritizes wavelength flatness. Table 5 shows the color difference (ΔE ₀₀ ) between the dimming state (plot) and the transmitting state (origin) when each control light source shown in FIG. 8 is used.

This indicates that even when the same EC compounds are combined, prioritizing NWD _Max as in the present invention can suppress light source effects more effectively than prioritizing wavelength flatness. Specifically, it was found that light source effects could be suppressed by 2.8 to 11 times for all five reference light sources, from low to high color temperatures. Furthermore, when the EC element of the example was installed as a variable ND filter in a camera having an image sensor, a sensory evaluation of simulated images was performed when the light source was changed. The EC element of the example was recognized as having minimal discomfort when comparing images in the transmission state and dimming state of the element, both for the reference light source and the reference light source. This indicates that good color reproducibility can be achieved by setting the NWD _Max value to 1.03 or less using the variable transmittance VT(λ) normalized to an average change of ND64.

Table 4 shows the NWD _Max values for the EC elements of Example 1 and Comparative Example 1 when the reference light source and the control light source were changed. FIG. 9 also shows the results of evaluating the influence of the light source on color reproducibility in the same manner as above.

A comparison of Table 4 confirms that the EC element of Example 1 is more capable of handling medium and low color temperatures than the EC element of Comparative Example 1. Furthermore, FIG. 9 shows that the plot for Example 1 in the dimmed state of the reference light source is closer to the origin (transmitted state) than the plot for Comparative Example 1. This indicates that the EC element of Example 1 is able to reduce the influence of the light source on color reproducibility more than the EC element of Comparative Example 1. Table 7 shows the color difference (ΔE ₀₀ ) between the dimmed state (plot) and the transmitted state (origin) when each reference light source shown in FIG. 9 is used.

This indicates that even when the same EC compounds are combined, prioritizing NWD _Max as in the present invention can suppress light source effects more effectively than prioritizing wavelength flatness. Specifically, it was found that light source effects could be suppressed by 2.1 to 3.2 times for all three reference light sources. Furthermore, when the EC element of the example was installed as a variable ND filter in a camera having an image sensor, a sensory evaluation of simulated images was performed when the light source was changed. The EC element of the example was recognized as having minimal discomfort when comparing images in the transmission state and dimming state of the element, both for the reference light source and the control light source. This indicates that good color reproducibility can be achieved by setting the NWD _Max value to 1.03 or less using the variable transmittance VT(λ) normalized to an average change of ND64.

(Examples 2 and 3)
10 shows the VT(λ) of the EC elements of Examples 2 and 3, in which the EC layers were constructed with different compositions (concentration ratios) using the same EC compounds as in Example 1. The wavelength flatness TF in the detection light wavelength range was 110% for Example 2 and 97.5% for Example 3. Table 6 shows the dimmed-state concentration (unit: mmol/L) of each EC compound, and the sum of the charge concentrations of the anodic and cathodic EC compounds.

Table 6 confirms that the total dimmed-state charge concentrations of the anodic EC compounds and the cathodic EC compounds in Examples 2 and 3 were approximately equal, at 66.5 mmol/L and 66.6 mmol/L, and 67.6 mmol/L and 67.5 mmol/L, respectively. Table 7 shows the NWD _Max and wavelength flatness TF values calculated using the daytime natural light spectrum shown in Figure 3(a) as the reference light source and a halogen lamp as the control light source. Table 7 also lists the NWD _Max and wavelength flatness TF values for Example 1 (prioritizing NWD _Max ) and Comparative Example 1 (prioritizing wavelength flatness), which were constructed using the same compound group.

Table 7 confirms that the EC elements of Examples 1 to 3 are more capable of handling medium and low color temperatures than the EC element of Comparative Example 1.

Figure 11 shows the results of evaluating the light source influence on color reproducibility for each of the EC elements of Examples 1 to 3 and Comparative Example 1, when daytime natural light shown in Figure 3(a) was used as the reference light source and a halogen lamp was used as the control light source. Figure 11 shows that the plots for the dimmed state of the control light source are closer to the origin (transmitted state) for Examples 1 to 3 than for Comparative Example 1. This shows that the EC elements of Examples 1 to 3, which prioritize NWD _Max , are able to reduce the light source influence on color reproducibility more than the EC element of Comparative Example 1, which prioritizes wavelength flatness. Table 7 shows the color difference (ΔE ₀₀ ) between the dimmed state (plot) and the transmitted state (origin) shown in Figure 11.

Table 7 shows that, even when the same EC compounds are combined, a composition prioritizing NWD _Max , as in the present invention, can suppress light source effects compared to a composition prioritizing wavelength flatness. Specifically, it was found that light source effects could be suppressed by approximately three times or more for all three concentration ratios. Furthermore, when the EC element of the example was installed as a variable ND filter in a camera having an image sensor, a sensory evaluation of simulated images was performed when the light source was changed. The EC element of the example was recognized as having minimal discomfort when comparing images in the transmission state and dimming state of the element, both for the reference light source and the control light source. This shows that good color reproducibility can be achieved by setting the NWD _Max value to 1.03 or less using the variable transmittance VT(λ) normalized so that the average change is ND64.

EC devices in Examples 4 and 5 and Comparative Examples 2 and 3 were fabricated by varying the combination and composition of EC compounds with the spectra shown in Figure 4. In Example 4 and Comparative Example 2, the EC layer was constructed using anodic EC compounds (1), (4), and (5) and cathodic EC compounds (6), (7), and (9). In Example 5 and Comparative Example 3, the EC layer was constructed using anodic EC compounds (1), (2), and (3) and cathodic EC compounds (8), (9), and (10). EC compounds (6) to (10) have peaks in the R region of the photodetector, EC compounds (2) to (4) have peaks in the G region of the photodetector, and EC compounds (1), (5), (6), and (8) have peaks in the B region of the photodetector. The extinction ratio between the transmitted and extinction states of each EC device was 64 (= average variable transmittance of 1.56%). The detection light wavelength range of the photodetector was the 425 nm to 680 nm range of the photodetector shown in Figure 2(a).

Figure 12 shows the variable transmittance VT(λ) spectra for Examples 4 and 5 and Comparative Examples 2 and 3. Table 8 shows the dimmed-state concentration (unit: mmol/L) of each EC compound, as well as the total charge concentration of the anodic EC compound and cathodic EC compound.

Table 8 confirms that the total dimmed state charge concentration of the anodic EC compound and the total dimmed state charge concentration of the cathodic EC compound in Examples 4 and 5 are approximately equal, at 68.3 mmol/L and 63.5 mmol/L, respectively. It also confirms that the total dimmed state charge concentration of the anodic EC compound and the total dimmed state charge concentration of the cathodic EC compound in Comparative Examples 2 and 3 are approximately equal, at 66.6 mmol/L, 66.7 mmol/L, and 61.3 mmol/L, respectively.

Furthermore, the NWD _Max values calculated using the spectrum of daytime natural light shown in Figure 3(a) as the reference light source and a halogen lamp as the control light source are shown in Table 9. From Table 9, it can be confirmed that Examples 1, 4, and 5 can accommodate medium and low color temperatures.

Figure 13 shows the results of evaluating the light source influence on color reproducibility of each EC element of Examples 1, 4, and 5 and Comparative Examples 1, 2, and 3. As can be seen from Figure 13, the plots of the dimmed state of the control light source are closer to the origin (transmitted state) for Examples 1, 4, and 5 than for Comparative Examples 1, 2, and 3. This shows that the EC elements of Examples 1, 4, and 5, which prioritize NWD _Max , are able to reduce the light source influence on color reproducibility more than the EC elements of Comparative Examples 1, 2, and 3, which prioritize wavelength flatness. Table 9 shows the color difference (ΔE ₀₀ ) between the dimmed state (plot) and the transmitted state (origin) shown in Figure 13.

Table 12 shows that, even when different EC compounds are used, prioritizing NWD _Max as in the present invention can suppress the light source effect on color reproducibility compared to prioritizing wavelength flatness. Specifically, it was found that the light source effect could be suppressed by approximately 2.4 times or more for all three compound combinations. Furthermore, when the EC element of the example was installed as a variable ND filter in a camera having an image sensor, a sensory evaluation of simulated images was performed when the light source was changed. The EC element of the example was recognized as having little discomfort when comparing images in the transmission state and dimming state of the element, both for the reference light source and the control light source. From this, it was found that good color reproducibility can be obtained by setting the NWD _Max value to 1.03 or less using the variable transmittance VT(λ) normalized so that the average change is ND64.

Example 6
Figure 15 shows the VT(λ) of the EC element of Example 6, in which the EC layer was constructed with a different composition (concentration ratio) using the same EC compounds as in Comparative Example 3. The wavelength flatness TF in the detection light wavelength range was 130%. Table 10 shows the dimmed concentration (unit: mmol/L) of each EC compound, as well as the sum of the charge concentrations of the anodic and cathodic EC compounds.

Table 10 confirms that the total charge concentration in the dimmed state of the anodic EC compound in Example 6 and the total charge concentration in the dimmed state of the cathodic EC compound are approximately equal, at 60.2 mmol/L and 60.2 mmol/L, respectively.

Table 11 shows the NWD _{Max and wavelength flatness TF values calculated using the spectrum of daytime natural light shown in Fig. 3(a) as the reference light source and the daylight white fluorescent lamp shown in Fig. 14 as the control light source. Table 11 also shows the NWD Max and} wavelength flatness of Comparative Example 3 (priority given to wavelength flatness) which was constructed using the same compound group.

Table 11 confirms that the EC elements of Examples 1 to 3 are more adaptable to fluorescent lamps with spectra with greater intensity fluctuations in the mid-color temperature range than the EC element of Comparative Example 1.

FIG. 16 shows the results of evaluating the light source influence on color reproducibility for each of the EC elements of Example 6 and Comparative Example 3, when daytime natural light shown in FIG. 3( a) was used as the reference light source and a daylight white fluorescent lamp shown in FIG. 14 was used as the control light source. As shown in FIG. 16, the plot of the dimmed state of the control light source is closer to the origin (transmitted state) for Example 6 than for Comparative Example 3. This shows that the EC element of Example 6, which prioritizes NWD _Max , is able to reduce the light source influence on color reproducibility more than the EC element of Comparative Example 3, which prioritizes wavelength flatness. Table 11 shows the color difference (ΔE ₀₀ ) between the dimmed state (plot) and the transmitted state (origin) shown in FIG. 16 .

Table 11 shows that, even when the same EC compounds are combined, a composition prioritizing NWD _Max , as in the present invention, can suppress light source effects compared to a composition prioritizing wavelength flatness. Specifically, when the spectrum of daytime natural light, which has relatively little intensity change, is used as the reference light source and a fluorescent light source, which has a spectrum with large intensity fluctuations, is used as the control light source, it was found that light source effects can be suppressed by approximately 26 times. Furthermore, when the EC element of the example was installed as a variable ND filter in a camera having an image sensor, a sensory evaluation of simulated images was performed when the light source was changed. The EC element of the example was recognized as having little discomfort when comparing images in the transmission state and the dimming state of the element, both for the reference light source and the control light source. This shows that good color reproducibility can be obtained by setting the NWD _Max value to 1.03 or less using the variable transmittance VT(λ) normalized so that the average change is ND64.

Claims (17)

An optical device having a photodetector and a photochromic element having a plurality of compounds whose light absorption characteristics change in response to an external stimulus,
the plurality of compounds are compounds having different absorption wavelengths,
the light-adjusting element has a variable transmittance VT(λ) that is a combination of the light absorption characteristics of the plurality of compounds;
the photodetector has a detection light wavelength range of x bar: 580 nm to 680 nm, y bar: 500 nm to 580 nm, and z bar: 425 nm to 500 nm in CIE color matching functions;
The reference illuminant is selected from CIE D65, D55, D50, Illuminant B, and Illuminant C;
When the reference illuminant is CIE A illuminant,
An optical device characterized in that NWD _Max < NWD _MaxFP .
NWD _Max : the maximum value of the ratio of the signal intensity ratio of the transmitted light for each wavelength region of the detection light incident on the photodetector in the transmission state and the dimming state of the dimming element, between the reference light source and the reference light source (reference light source/reference light source or reference light source/reference light source); NWD _MaxFP : the NWD _Max at the concentration ratio of the plurality of compounds at which the wavelength flatness TF of the VT(λ) in the wavelength region of the detection light is the minimum value TF _FP; 2. The optical device according to claim 1, wherein the variable transmittance VT(λ) is expressed by the following formula:
Δε _m (λ): the change extinction coefficient of compound m (m is 1 to the total number of compounds)
C _m : concentration of compound m in the dimmed state L : optical path length of the dimming element [m] 3. The optical device according to claim 1, wherein NWD _Max is the maximum value among NW _R1 /NW _R0 , NW _R0 /NW _R1 , NW _B1 /NW _B0 , and NW _B0 /NW _B1 .
NW _R0 : change in the detection signal ratio in the photodetector of the red wavelength region of the transmitted light emitted from the reference light source and transmitted through the light control element NW _R1 : change in the detection signal ratio in the photodetector of the red wavelength region of the transmitted light emitted from the control light source and transmitted through the light control element NW _B0 : change in the detection signal ratio in the photodetector of the blue wavelength region of the transmitted light emitted from the reference light source and transmitted through the light control element NW _B1 : change in the detection signal ratio in the photodetector of the blue wavelength region of the transmitted light emitted from the control light source and transmitted through the light control element NW _R0 = W _RC0 /W _RT0
NW _R1 =W _RC1 /W _RT1
NW _B0 =W _BC0 /W _BT0
NW _B1 =W _BC1 /W _BT1
WRC0 = _SGC0 / _SRC0
WRC1 = _SGC1 / _SRC1
W _RT0 = S _GT0 / S _RT0
W _RT1 = S _GT1 / S _RT1
W _BC0 = S _GC0 / S _BC0
W _BC1 = S _GC1 / S _BC1
WBT0 = _SGT0 / _SBT0
WBT1 = _SGT1 / _SBT1
S _RT0 , S _RT1 : Detected signal intensities S _GT0 , S _GT1 in the red wavelength region of transmitted light emitted from the reference light source and the control light source and transmitted through the light control element in the transmission state, at the photodetector; S _BT0 , S _BT1 : Detected signal intensities S BT0 , S BT1 in the green wavelength region of transmitted light emitted from the reference light source and the control light source and transmitted through the light control element in the transmission state, at the photodetector; S _RC0 , S _RC1 : Detected signal intensities S GC0 , S GC1 in the red wavelength region of transmitted light emitted from the reference light source and the control light source and transmitted through the light control element in the dimming state, at the photodetector; S _BC0 , S _BC1 in the green wavelength region of transmitted light emitted from the reference light source and the control light source and transmitted through the light control element in the dimming state, at _{the photodetector} . : Detected signal intensity in the photodetector of the blue wavelength region of transmitted light emitted from the reference light source and the control light source and transmitted through the dimming element in the dimming state 4. The optical device according to claim 1, wherein the NWD _Max is 1.03 or less using the variable transmittance VT([lambda]) normalized so that the amount of change is 1/64. An optical device described in any one of claims 1 to 4, characterized in that the multiple compounds are compounds whose light absorption characteristics change electrically. An optical device described in any one of claims 1 to 5, characterized in that the multiple compounds are electrochromic compounds. An optical device described in any one of claims 1 to 6, characterized in that the multiple compounds are three or more compounds. the plurality of compounds are anodic electrochromic compounds and cathodic electrochromic compounds;
8. The optical device according to claim 1, wherein the sum of the charge densities of the anodic electrochromic compounds in the dimmed state is approximately equal to the sum of the charge densities of the cathodic electrochromic compounds in the dimmed state. The optical device described in claim 8, characterized in that it has multiple anodic electrochromic compounds and multiple cathodic electrochromic compounds. An optical device according to any one of claims 1 to 9, characterized in that at least one of the compounds selected from the plurality of compounds has a peak of a variable absorption spectrum in each of the plurality of detection light wavelength ranges of the photodetector. 11. The optical device according to claim 1, wherein the reference illuminant is selected from the group consisting of D50 , D55, D65, B illuminant, and C illuminant. 12. The optical device according to claim 1 , wherein the dimming element has a dimming ratio, which is a ratio of the transmitting state to the dimming state, of 8 or more. 13. The optical device according to claim 12 , wherein the extinction ratio is 32 or more. The optical device according to any one of claims 1 to 13 , wherein the dimming element satisfies TF>TF _FP . The optical device according to any one of claims 1 to 14 , wherein the photodetector is an image sensor. An imaging device having an optical system having a plurality of lenses and the optical device described in claim 15 , characterized in that the imaging element receives light that has passed through the optical system, and the dimming element is arranged between the optical system and the imaging element as an optical filter. the imaging optical system further includes a plurality of lenses, and the light control element and the imaging optical system form a lens unit;
16. The optical device according to claim 1, wherein the lens unit is arranged so that light passing through the lens unit is incident on the photodetector.