JP2796337B2 - Light source device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source device, and relates to a technique effective when applied to a light source device such as a liquid crystal display device that requires a surface light source.

[Conventional technology]

A conventional planar light source device is described in JP-B-58-17957. The outline is shown in FIG. A light source 4B is arranged on one end surface of the transparent substrate A, the transparent substrate 4A is made of a material having good light transmission, one surface 4a on the observer side is made a smooth surface, and the other surface 4b opposed thereto is made a rough surface. doing. This rough surface 4b
Is configured to diffuse the light from the light source 4B and reflect the light from the light source 4B to the smooth surface 4a. The transparent substrate 4A is formed of an inclined plane such that the thickness decreases as the distance from the light source 4B increases.

[Problems to be solved by the invention]

In the prior art, as shown in FIG. 7, the thickness of the transparent substrate decreases as X increases, and the light source 4B, for example, a fluorescent tube or the like is used on one end surface of the transparent substrate 4A. (A) As a planar light source having a relatively small area, a single fluorescent tube is used as shown in FIG.
(B) In the case of a large area, the fluorescent tube has a two-story configuration shown in FIG. 8 to obtain a large-area and high-luminance surface light source. However, in these prior arts, it is difficult to cope with high luminance and large area even in the case of (a) even though it is thin and lightweight, and in (b), it is difficult to cope with high luminance and large area. Even with a surface light source, there has been a problem that it is difficult to realize it in terms of thinness and weight reduction. SUMMARY OF THE INVENTION An object of the present invention is to provide a technique capable of obtaining a large-area, light-weight, thin, and high-intensity surface light source that is uniform over the entire screen.

[Means for solving the problem]

An object of the present invention is to provide a light source device in which light sources are arranged at both end portions of a transparent substrate, and to observe the transparent substrate so that a change in the amount of light per unit area on an observation surface remote from the light source can be suppressed within a certain level range. The surface on the user side is composed of an inclined curved surface,
A rough surface is formed on one surface of the transparent substrate but on the inclined curved surface so as to diffuse the incident light, and a plane as the other surface of the transparent substrate has a stripe shape having a predetermined width across the center between the light sources. This is achieved by forming a mirror surface and making the remaining part rough, and providing a reflective layer having high brightness opposite the flat part.

[Action]

According to the above-described means, a surface light source having a large area and high luminance can be obtained by disposing the light sources on both sides.
In addition, since the inclined curved surface of the transparent substrate is provided on the viewer side, a space is formed between the thinnest portion of the transparent substrate and the uniform diffusion layer on the inclined curved surface. It is possible to prevent luminance nonuniformity caused by combining light beams incident from the light source. Further, the transparent substrate,
In the plan view which is the end face portion where the light source is arranged and the other surface, the surface is roughened except for a band-like portion substantially along the thinnest portion, so that the brightness is not low when viewed from the diffusion layer side. Uniformity is lost, and a light source having uniform luminance can be obtained. The reason why the belt-like portion in the flat portion is made a mirror surface without roughening is to prevent the luminance at the central portion from becoming too high by allowing light to escape from the portion once to the outside of the substrate. Light emitted from the mirror surface is reflected by the reflector and re-enters the transparent substrate. At this time, light is lost, and as a result, the brightness at the center can be reduced.

〔Example〕

Hereinafter, the configuration of the present invention will be described together with an embodiment in which the present invention is applied to a light source device of a liquid crystal display device. In all the drawings for explaining the embodiments, parts having identical functions are given same symbols and their repeated explanation is omitted.

A liquid crystal display device and a light source device according to an embodiment of the present invention are shown in FIG. 1 (cross-sectional view) and FIG. 2 (exploded perspective view).

As shown in FIGS. 1 and 2, the liquid crystal display device comprises:
Lower frame (mold case) 1 and upper frame (cover) 2
Each of the liquid crystal display panel 3 and the light source device 4 is provided in the interior defined by the above.

The lower frame 1 is formed in a square shape, and is formed of, for example, a resin material. The upper frame 2 is formed in a square shape to be fitted with the lower frame 1. The upper frame 2 has an opening 2A at the center. The opening 2A is the liquid crystal panel 3
Is configured to be exposed. The upper frame 2 is made of, for example, a metal material such as iron or an aluminum alloy, or a resin material.

Although not shown in detail, the liquid crystal display panel 3 is driven by a dot matrix type time division system, or
It is composed of one driven by TFT. The liquid crystal display panel 3 has a lower transparent glass substrate 3B and an upper transparent glass substrate 3C.
The liquid crystal unit 3A is provided in the space between the two. The liquid crystal unit 3A
Liquid crystal regulated by an alignment film formed on the inner (liquid crystal side) surface of each of the lower transparent glass substrate 3B and the upper transparent glass substrate 3C is sealed. As the liquid crystal of the liquid crystal unit 3A, a twisted nematic type liquid crystal is used. The liquid crystal of the liquid crystal unit 3A is configured so that the lighting display is controlled by the scanning electrodes formed on the inner surface of the lower transparent glass substrate 3B and the display electrodes formed on the inner surface of the upper glass substrate 3C. . A polarizing plate 3D is provided on the outer surface of the lower transparent glass substrate 3B, and a polarizing plate 3E is provided on the outer surface of the upper transparent glass substrate 3C.

As shown in FIG. 3 (a perspective view from the lower side of the liquid crystal display device), the display electrode is detachably attached (fitted) to the bottom of the lower frame 1 (a segment driver circuit 5B). And driven at 5C. In the liquid crystal display panel 3 of the present embodiment, since the display electrodes are vertically divided into two, the segment driver circuits 5B and 5C are provided. Each of the segment driver circuits 5B and 5C is formed of a wiring board (for example, a glass epoxy resin) on which a semiconductor device for a segment driver is mounted.

The scanning electrodes are driven by a common driver circuit 5A detachably attached to the bottom of the lower frame 1. This common driver circuit 5A includes the segment driver circuit 5B and
Like 5C, it is composed of a wiring board on which a semiconductor device is mounted.

Each of the segment driver circuits 5B and 5C and the common driver circuit 5A is driven by a liquid crystal (LCD) driving power supply circuit and a timing generation circuit. Similarly, the liquid crystal driving circuit 5D is configured by a wiring board on which a semiconductor device and passive elements such as resistors and capacitors are mounted.

The light source device 4 is, as shown in FIGS.
It mainly comprises a transparent substrate 4A, a light source 4B, a light source reflector 4C, a transparent substrate reflector 4D, and an inverter power supply circuit 4E. The 4E may not be built in the liquid crystal module.

As shown in detail in FIG. 4 (a perspective view of the transparent substrate viewed obliquely from above), the transparent substrate 4A is made of a light-transmitting rectangular transmission material. The transparent substrate 4A is made of an acrylic resin having a light transmittance of about 90 to 95%. Further, the transparent substrate 4A may be made of a transparent glass material. In this embodiment, the width W of the transparent substrate 4A is 250 mm,
The length direction is 160 [mm].

The surface 4b of the transparent substrate 4A on the side of the diffusion plate 6 is formed as an inclined curved surface so that the light incident on the diffusion plate does not significantly decrease even if it is separated from the light source. In other words, the transparent substrate 4A is
It is constituted by a continuous inclined curved surface that becomes thinner (from the dimension H to the dimension h) as the distance from the surface increases. This inclined curved surface 4b can be substantially expressed by the following equation.

Y ₂ = h (2) L / 2−d ≦ X ≦ L / 2 where Y ₁ , Y ₂ : distance in H or h direction X: distance in L direction from light source 4B L = 160 mm n = 2-3 is optimal h = 0.5-3mm d = 0.5-10.0mm (In the range of L / 2 ≦ X ≦ L, Y ₁ and Y ₂ are related to X = L / 2.
It becomes a line symmetric curve. As described above, by properly selecting the curved surface 4b, it should be theoretically possible to obtain a uniform surface luminance.
Actually, there is a manufacturing error, and there is a disadvantage that uniformity of luminance is lost due to a slight change in the curved surface. In order to make the in-plane luminance more uniform, not only optimize the curved surface 4b,
It is effective to roughen the entire surface of the transparent substrate except for two end surfaces facing the light source 4B. This rough surface is, for example, 20-
It has a roughness substantially equal to the surface formed by cutting with a file of about 400 files. When the transparent substrate is molded by injection molding, the rough surface (the pitch of the mat and the depth of the groove) can be easily controlled by forming a mat surface, which is excellent in moldability and preferable in view of workability. . But,
Even in this case, it is unavoidable that the luminance distribution is affected by the manufacturing error. In order to suppress variations in the luminance distribution due to manufacturing errors, a curved surface is set in advance so that the luminance increases at the center, and the high luminance at the center is equalized by the following means.

FIG. 5 shows an example of a transparent substrate 4A that provides such means. FIG. 5 is a view of the transparent substrate 4A and the light source section 4B as viewed from the plane section 4a side. The hatched portion in the figure is a roughened portion. That is, a non-roughened mirror-like region is formed with a width of 2 across the center line with respect to the plane portion 4a. The light diffused in the transparent substrate passes through the mirror portion and goes to the reflection plate 4D. This light is reflected by the reflector 4D, passes through the mirror, and returns to the transparent substrate.
Although the light is incident on 4A, light loss occurs at the time of reflection and incidence at this time, and as a result, light traveling toward the diffusion plate 4D side can be reduced in the central portion, and the in-plane luminance distribution can be made uniform. In this case, the width 2 of the mirror surface portion may be substantially equal to the width 2d of the flat portion near the center of the curved surface portion 4b.

FIG. 6 shows a state in which the in-plane luminance distribution is made substantially uniform by providing a mirror portion having a width of 2 = 8 mm on the 4a side. The in-plane luminance distribution in the figure is a result measured from above the diffusion plate 6. In FIG. 6, d, H, L, and h are the same as the definitions in the first equation, and are 4.0 mm, 7.0 mm, 160 mm, and 1.6 mm, respectively. The curved surface 4b in FIG. 6 is represented by a curved surface when n = 2.3 in the first and second equations.

Also, d = 1.

As the light source 4B, for example, a cold cathode ray tube having a length of about 270 [mm] is used. This cold cathode ray tube is driven by an inverter power supply circuit 4E attached to the bottom of the lower frame 1. The inverter power supply circuit 4E is configured to convert, for example, a DC power supply of 5 to 30 [V] to an AC power supply of 30 to 50 [KHz] at 300 to 400V. The inverter power supply circuit 4E is composed of a wiring board on which a semiconductor device and the like are mounted as in the circuits 5A to 5D.

The light source reflector 4C covers the light source 4B except for a part of the light source 4B so that the light of the light source 4B can be efficiently reflected in the direction of the transparent substrate 4A, and has a U-shaped or U-shaped cross section. . The reflector 4C for a light source is made of, for example, an aluminum plate having a surface (surface on the light source 4B side) coated with a white paint (acrylic resin paint). In particular, the brightness L * value of the white paint is desirably 94 or more. (However, the L * value is the lightness index in the CIE ULCS color system.) The reflector 4D is placed on the plane 4a of the transparent substrate 4A so that the light of the light source 4B can be efficiently reflected to the liquid crystal panel 3 side. It is configured. The substrate reflection plate 4D is made of, for example, the same material as the light source reflection plate 4C. Also in this case, the lightness L * value of the reflection plate is preferably as high as possible, preferably 94 or more.

A light diffusion plate 6 is provided between the liquid crystal panel 3 and the transparent substrate 4A of the light source device 4. This acrylic resin is thick
It is desirable that the surface is roughly 0.5 to 3.0 mm and both surfaces are roughened.

A plurality of light sources 4B of the present invention may be arranged at each end,
Moreover, you may comprise by LED.

In the above description, the inclined curved surface 4b is represented by an exponential function. However, this may be approximately an exponential function. Can be obtained.

Since the light source device 4 of the present invention can obtain high luminance, it is effective when the liquid crystal display panel 3 of the liquid crystal display device is configured in a super twisted nematic type white & black mode (light transmittance is low). .

The present invention is not limited to a liquid crystal display element, but can be applied to all light source devices requiring a surface light source, such as a light source device of a measuring instrument.

〔The invention's effect〕

According to the present invention, a surface light source having high luminance and uniform luminance can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view when a light source device according to an embodiment of the present invention is used for a liquid crystal display element, and FIG. 2 is an embodiment of the present invention shown in FIG. FIG. 3 is a rear perspective view of a liquid crystal display device according to an embodiment of the present invention. FIG. 4 is a perspective view showing a main part of a light source device according to an embodiment of the present invention. FIG. 6 is a rear view of a main part of the light source device shown in FIG. 4, FIG. 6 is a luminance distribution diagram of the light source device according to the present invention, and FIG. 7 and FIG. is there. 3 Liquid crystal display panel, 3A Liquid crystal part, 4 Light source device, 4A Transparent substrate, 4B Light source, 4C Reflector for light source, 4D Reflector for substrate, 4E Inverter Power circuit,
4a: Plan view, 4b: Curved surface.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Kiyohe Kinukawa 3300 Hayano Mobara-shi, Chiba Pref. Mochi Plant, Hitachi Co., Ltd. (56) References Japanese Utility Model Sho 62-65676 (JP, U) Japanese Utility Model Sho 62- 32836 (JP, U) Real opening 63-26873 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G09F 9/00 336 G09F 9/00 332

Claims (3)

(57) [Claims] 1. A liquid crystal display device having a liquid crystal display element and a light source device for irradiating the liquid crystal display element from the back, wherein the light source device has a transparent substrate having a light transmitting property, and the transparent substrate is opposed to the first substrate. And a second surface, light sources are disposed at both end portions of the transparent substrate, the first surface is a light diffusing surface, and the first surface of the transparent substrate is located between the light sources. The second surface side is a flat surface, the central portion between the light sources is a mirror surface, and the remaining portions on the second both sides are A liquid crystal display device having a light diffusion surface. 2. The method according to claim 1, wherein the inclined curved surface of the transparent substrate is represented by an exponential function of a distance from each of the light sources, and is symmetrical with respect to a central portion of each of the light sources.
The liquid crystal display device according to the item. 3. The method according to claim 1, further comprising:
2. The liquid crystal according to claim 1, wherein the surface of the second surface is substantially flat, and the mirror surface portion of the second surface is formed to substantially face the flat surface of the thinnest portion. Display device.