JP3067149B2 - Illumination device and liquid crystal display using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention mainly relates to a thin backlight device for a liquid crystal display incorporated in a computer, a word processor, and a liquid crystal television.

[Conventional technology]

Heretofore, there has been known a system in which an irregular reflection surface is formed by a milky white halftone dot on a transparent plate as described in JP-A-63-62105.

[Problems to be solved by the invention]

However, when such a conventional lighting device is set behind a liquid crystal display and turned on, the luminous efficiency is low, and it is necessary to stack a plurality of transparent plates in order to increase the surface light emission luminance. As a result, the lighting device is thick. However, there is a problem that the liquid crystal screen is easily uneven because it is difficult to obtain a flat in-plane luminance distribution.

Therefore, the present invention solves such a conventional problem, and an object of the present invention is to provide a thin illuminating device that uses only one thin transparent plate, has high luminous efficiency, and can obtain a flat luminance distribution. It is in.

[Means for solving the problem]

In order to solve the above problems, the lighting device of the present invention is a transparent plate provided with a diffuse reflection surface having a diffuse reflection portion on at least one surface, a light source arranged along four sides of the transparent plate, A diffuser disposed on the light-emitting side of the transparent plate, wherein the diffusely reflecting portion comprises a plurality of fine lines, and the plurality of fine lines are parallel to a side of the transparent plate adjacent to the light source. , The pitch is constant, and the fine lines are arranged such that the line widths of the fine lines differ depending on the distance from the light source.

Also, on at least one surface, a transparent plate provided with a diffuse reflection surface having a diffuse reflection portion, a light source disposed along four sides of the transparent plate, and a diffusion plate disposed on the light exit side of the transparent plate. , The irregular reflection portion is composed of a plurality of fine lines, the plurality of fine lines are parallel to the side of the transparent plate adjacent to the light source, the line width is constant, and the light source Characterized in that the fine lines are arranged such that the pitch between the fine lines varies depending on the distance from the line.

Further, at least one surface has a transparent plate provided with a diffuse reflection surface having a diffuse reflection portion, a light source disposed along the transparent plate, and a diffusion plate disposed on the light exit side of the transparent plate. In the lighting device, the irregular reflection portion includes a plurality of fine lines, and the fine lines have a constant pitch and are curved.

Further, at least one surface has a transparent plate provided with a diffuse reflection surface having a diffuse reflection portion, a light source disposed along the transparent plate, and a diffusion plate disposed on the light exit side of the transparent plate. In the lighting device, the irregular reflection portion includes a plurality of fine lines, and the fine lines have a constant pitch, and
It is a curved straight line.

Furthermore, a liquid crystal display of the present invention includes the above-described lighting device of the present invention.

(Operation)

In the lighting device described above, light incident from the light introduction end face of the transparent plate travels while being substantially totally reflected in the transparent plate having a refractive index larger than air, and light hitting the milky white thin line there. The light is diffusely reflected and is emitted from the transparent plate. Therefore, the intensity and distribution of the emitted light vary depending on the pattern and arrangement of the thin lines, and the design of the irregular reflection portion greatly affects the illumination quality.
This will be described in detail in comparison with the prior art.

In general, a backlight device for a liquid crystal display device is required to be bright and have no unevenness in brightness. In a so-called edge light type illuminating device which constitutes a planar illuminating device by making light incident on the end face of the transparent plate and guiding the light inside the transparent plate like the illuminating device of the present invention, irregular reflection provided on the transparent plate By increasing the amount of irregular reflection on the surface, the total amount of emitted light can be increased, that is, bright illumination can be obtained. However, if the amount of irregular reflection is blindly increased, the brightness rapidly decreases as the distance from the light source increases, and as a result, luminance unevenness in a light emitting surface used for illumination becomes large.

As a countermeasure against this, the diffuse reflection surface may be composed of a diffuse reflection portion and a total reflection portion, and the diffuse reflection portion and the total reflection portion may be delicately arranged so that each has no luminance unevenness and has high overall light emission efficiency and bright illumination. .

In the above prior art, this is embodied by forming a milky white halftone dot on a transparent plate, but it is difficult to increase the area ratio of the irregular reflection portion to the total reflection portion (hereinafter referred to as the area ratio) by this method. Light emission efficiency tends to be low.

Further, when a manufacturing error occurs with respect to the design size of the target halftone dot, the area ratio changes with the square of this error, and therefore, there is a serious drawback that an illuminating device particularly has a large variation in luminance unevenness.

On the other hand, in the lighting device according to the configuration of the present invention, it is possible to increase the total light emission efficiency because the area ratio can be set as long as only the width of the milky white thin line is changed. On the other hand, even if a manufacturing error occurs, the change in the area ratio can be suppressed only in proportion to the error, so that a lighting device with small luminance variation can be realized in the first place.

In recent years, simulation techniques such as ray tracing using a computer have been developed, and it has become possible to optimally design an optical system with high precision. is there.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing one embodiment of the present invention. Reference numeral 2 denotes a light source, which uses a rod-shaped fluorescent discharge tube, but may be one in which LEDs are arranged in a straight line. The light source 2 is disposed adjacent to the end face 20 of the transparent plate 1, and a light beam is guided from the light source 2 to the transparent plate 1. In this case, a plate made of PMMA resin having a uniform thickness of 1.0 to 5.0 mm was used for the transparent plate 1, but materials such as polycarbonate, polystyrene, and glass can also be used. The diffuse reflection surface 3 was formed on one surface of the transparent plate. In this case, a white thin line having a constant width was printed by silk screen printing. A method other than printing, for example, a method of masking the transparent plate 1 and painting it white or attaching a white tape with an adhesive may be used.
The transparent plate 1 is set in a state sandwiched between the diffusion plate 4 and the reflection plate 5, and the light introduced from the end face 20 is diffused from the irregular reflection surface 3.
The light travels while repeating reflection and scattering between the light and the total reflection surface 6. As described above, since the irregular reflection surface 3 is composed of the total reflection portion 10 and the irregular reflection portion 11 formed of a milky white thin line, the light spreads not only in the vicinity of the introduction end face but also in the entire region of the transparent plate 1 and exits to the diffusion plate 4 side. Therefore, the luminance distribution of the illumination light viewed from the side of the diffusion plate 4 became flat. Arrow A indicates the direction in which light comes out.

As shown in FIG. 10, the luminance distribution can be improved to some extent by the method of forming the irregular reflection surface with milky white dots as described in JP-A-63-62105, but this method increases the overall light emission efficiency. In order to do so, it is absolutely necessary to use a plurality of transparent plates 1 in an overlapping manner, and eventually the entire lighting device becomes thick. On the other hand, in the embodiment of the illuminating device according to the present invention shown in FIG. 1, the area ratio of the irregular reflection portion 11 to the total reflection portion 10 can be increased, and even if only one transparent plate 1 is used, it is very bright. In addition, a lighting device having a good luminance distribution can be made significantly thinner. FIG. 2 is a graph showing a luminance distribution when the lighting device of FIG. 1 is turned on, and the luminance of the upper surface of the diffusion plate 4 is measured by sweeping a luminance meter from B to C at a constant speed in FIG. It is. First
Further supplementing the embodiment of the figure, it is necessary to keep the print line width of the fine line within a certain range in order to remove uneven brightness in a narrow area by the diffusion plate 4 and obtain visually uniform illumination.
In this embodiment, the fine wire pitch is kept constant, for example, pitch 1.
The line width was set to about 0.1 to 0.5 mm with respect to 0 mm. When the pitch is 0.5 mm, the line width is set to about 0.05 to 0.25 mm. This is because if the area ratio is less than 10%, it is difficult to completely eliminate the uneven brightness in a narrow area, and furthermore, if the irregular reflection surface 3 is manufactured under the condition that the pits between lines and the line width are fixed to a certain value, This is because when the ratio exceeds 50%, the luminance is greatly reduced at the center of the diffusion plate, and the luminance unevenness is deteriorated.

The thickness of the printing ink is 1/100 to 7/100 mm, more preferably 2/100 to 5/100 mm. The printing ink used was a mixture of acrylic or urethane-based resin or UV-curable resin mixed with titanium oxide powder, etc.If the printing thickness was less than 1 / 100mm, the light passing through it increased and the diffuse reflection effect was reduced. If it is small and exceeds 7/100 mm, the degree of adhesion of the printing will be reduced and it will be easy to peel off or chip off, and it will be difficult to obtain dimensional accuracy.

FIG. 3 shows the irregular reflection surface 3 provided on the transparent plate 1 used in FIG.
FIG. The line width and pitch of the irregular reflection section 11 and the total reflection section 10 are arranged so that the absolute luminance is high and the luminance unevenness is reduced. Actually, when the external dimensions and thickness of the transparent plate 1 change, the optimum values of the pitch and the line width also change. Therefore, fine adjustment is required according to the dimensions of the transparent plate 1 and the allowable quality of illumination.

It has been found that the use of the illumination device using the linear pattern shown in FIG. 3 as the back illumination of the liquid crystal display has an effect that the displayed characters are easily read visually.

FIG. 4 and FIG. 5 are pattern diagrams of the irregular reflection surface of the embodiment in which the milky white thin line is constituted by a curved line or a curved straight line, respectively, which is suitable as illumination of a display for displaying images such as figures and pictures. .

FIG. 6 is an explanatory view showing an embodiment of the present invention in which the line width of each fine line is increased or decreased according to the distance from the light source, and shows a state in which the diffusion plate is removed for explanation. Diffuse reflection part
By forming the thin line 11 near the end face 20 and the wide line at the center of the transparent plate 1, it is possible to obtain a flatter luminance distribution than that of the embodiment of FIG. Also in this example, a PMMA resin plate having a uniform thickness of 1 to 5 mm was used as the transparent plate 1. Also in this case, the pitch of the thin wires is fixed, for example, 1 mm pitch, the line width is set to about 0.2 mm near the end face 20, and set to about 0.85 mm at the center of the transparent plate. If the pitch is 0.5 mm, the line width may be about 0.1 mm near the end face 20 and 0.4 to 0.45 mm at the center of the transparent plate.

As in the above example, good results could not be obtained with a line width of less than 0.05 mm and a line width of more than 0.85 mm when the pitch was 1.0 mm. This indicates that the visual luminance unevenness is not determined only by the line width, but that the ratio of the line width to the pitch dimension is important.
85%, preferably 10-80%, is suitable. The best results were obtained when the pitch dimension was set between about 0.5 and 1.5 mm.

Further, the line width is gradually increased from the thinnest line toward the center of the transparent plate, but a uniform luminance distribution cannot be obtained by simply increasing or decreasing the line width at a fixed ratio. It is necessary to optimize how to increase or decrease the size according to the size and thickness of the transparent plate.

In some cases, a special liquid crystal display is required to have an illumination with a slightly higher luminance at the center than at the periphery, but this case can be easily coped with by increasing or decreasing the line width.

FIG. 7 is a graph showing a luminance distribution when the lighting apparatus of FIG. 6 is turned on. For explanation, a diffusion plate omitted in the drawing is attached, and a luminance meter is moved at a constant speed from D to E on the diffusion plate. It was measured by sweeping. As a result, both the luminance distribution and the absolute luminance were improved as compared with FIG.

FIG. 8 is an explanatory view showing one embodiment in which light sources are arranged on four end faces of a transparent plate. When a liquid crystal display having a large light transmission loss is used, a slightly brighter illuminating device is required. In this embodiment, since four rod-like light sources 2 are used, a two-lamp type shown in FIG. 1 is used. More than twice the brightness as compared to the example.

FIG. 9 is an explanatory view showing an embodiment of the present invention in which the line pitch is increased or decreased according to the distance from the light source while keeping the line width of each fine line constant. Coarse pitch near the light source,
Since the portion far from the light source has a dense pitch, the brightness distribution of light can be equivalent to the result in the embodiment shown in FIG. In general, when a fine line pattern is formed by printing, the resulting print width accuracy tends to change depending on the size of the fine line width due to the influence of the surface tension of the ink. However, in the present embodiment shown in FIG. Since the printing was performed using the thin line, a printing error was extremely unlikely to occur, and a favorable result was obtained in which the variation in luminance was further reduced.

In this embodiment, a PMMA resin plate having a uniform thickness of 1 to 5 mm was used for the transparent plate 1. The line width of the irregular reflection part 11 is 0.1
0.30.3 mm is preferably set between 0.2 and 0.25 mm, and in this case, the pitch was made dense or coarse between 1.50 and 0.25 mm to achieve flat luminance.

〔The invention's effect〕

As described in detail above, the lighting device of the present invention includes: (1) a transparent plate provided with diffuse reflection composed of a diffuse reflection portion and a total reflection portion on at least one surface, and arranged along four sides of the transparent plate. A light source, and a diffusion plate disposed on the light exit side of the transparent plate, wherein the irregular reflection portion is composed of a plurality of fine lines, and the plurality of fine lines is the transparent adjacent to the light source. The fine lines are arranged so as to be parallel to the sides of the plate, have a constant pitch, and have different line widths depending on the distance from the light source.

(2) A transparent plate provided with a diffuse reflection surface comprising a diffuse reflection portion and a total reflection portion on at least one surface;
A lighting device comprising: a light source arranged along a side; and a diffusion plate arranged on a light emitting side of the transparent plate, wherein the irregular reflection portion includes a plurality of thin lines, and the plurality of thin lines are the light source. Are arranged in parallel to the sides of the transparent plate adjacent to the thin plate, the line width is constant, and the line pitch of the fine lines differs depending on the distance from the light source.

(3) a transparent plate provided with a diffuse reflection surface having a diffuse reflection portion on at least one surface, a light source disposed along the transparent plate, and a diffusion plate disposed on the light exit side of the transparent plate;
Wherein the irregular reflection portion comprises a plurality of fine lines, and the fine lines have a constant pitch and are curved.

(4) a transparent plate provided with a diffuse reflection surface having a diffuse reflection portion on at least one surface, a light source disposed along the transparent plate, and a diffusion plate disposed on the light exit side of the transparent plate;
Wherein the irregular reflection portion is composed of a plurality of fine lines, and the fine lines have a constant pitch and are bent straight lines.

With the above configuration, the luminaire with high overall luminous efficiency and flat luminance distribution is configured to be thinner than the conventional one.
This has a great effect that it can be provided, and a practical effect that it is possible to make the variation in lighting quality much smaller than the conventional one.

Also, if the illumination device of the present invention is used in which thin lines serving as irregular reflection portions are formed as straight lines as back illumination when displaying characters or the like on a liquid crystal display, the displayed characters can be visually very easily read. Have.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a lighting device of the present invention. FIG. 2 is a graph showing a luminance distribution when the lighting device of FIG. 1 is turned on. FIG. 3 is a detailed view of a diffuse reflection surface provided on the transparent plate used in the embodiment of FIG. FIG. 4 is an explanatory diagram of a pattern of an irregular reflection surface in which a milky white thin line is formed by a curve. FIG. 5 is an explanatory diagram of a pattern of a diffuse reflection surface constituted by a straight line obtained by bending a milky white thin line. FIG. 6 is an explanatory view showing an embodiment of the present invention in which the width of a thin line is increased or decreased according to the distance from a light source. FIG. 7 shows the sixth
The graph which shows the luminance distribution at the time of lighting the lighting device of a figure.
FIG. 8 is an explanatory view showing one embodiment of the present invention in which light sources are arranged on four end faces of a transparent plate. FIG. 9 is an explanatory diagram showing one embodiment of the present invention in which the line pitch is increased or decreased according to the distance from the light source while keeping the line width of the fine line constant. FIG. 10 is a perspective view showing an example of a conventionally used lighting device. DESCRIPTION OF SYMBOLS 1 ... Transparent plate 2 ... Light source 3 ... Diffuse reflection surface 4 ... Diffusion plate 5 ... Reflection plate 6 ... Total reflection surface 10 ... Total reflection part of diffuse reflection surface 11 ... Diffuse reflection part of diffuse reflection surface 20 ... Transparent plate end face 50

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F21V 8/00 601 G02F 1/13357 G02B 6/00 G09F 9/00 336

Claims (5)

(57) [Claims] 1. A transparent plate provided with a diffuse reflection surface having a diffuse reflection portion on at least one surface, a light source disposed along four sides of the transparent plate, and a diffuser disposed on a light emitting side of the transparent plate. And a plate, wherein the irregular reflection portion comprises a plurality of fine lines, and the plurality of fine lines are parallel to a side of the transparent plate adjacent to the light source, have a constant pitch, and A luminaire, wherein the fine lines are arranged so that the line widths thereof are different depending on the distance from a light source. 2. A transparent plate provided with a diffuse reflection surface having a diffuse reflection portion on at least one surface; a light source disposed along four sides of the transparent plate; and a light source disposed on a light emitting side of the transparent plate. A diffuser plate, wherein the irregular reflection portion is composed of a plurality of fine lines, and the plurality of fine lines are parallel to a side of the transparent plate adjacent to the light source, have a constant line width, and A lighting device, wherein the pitch between the thin lines is different depending on the distance from the light source. 3. A transparent plate provided with a diffuse reflection surface having a diffuse reflection portion on at least one surface, a light source disposed along the transparent plate, and a diffusion plate disposed on the light exit side of the transparent plate. , Wherein the irregular reflection portion comprises a plurality of fine lines, and the fine lines have a constant pitch and are curved. 4. A transparent plate having a diffuse reflection surface having a diffuse reflection portion on at least one surface, a light source disposed along the transparent plate, and a diffusion plate disposed on the light exit side of the transparent plate. , Wherein the irregular reflection portion comprises a plurality of fine lines, and the fine lines have a constant pitch and are bent straight lines. 5. A liquid crystal display using the lighting device according to claim 1.