JP2603649B2 - Surface lighting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a planar lighting device used for a light panel, a backlight of a liquid crystal display device, or the like, and requiring substantially uniform luminance on a light emitting surface.

[Background Art] In general, this type of planar lighting device has a plate-shaped light guide, and the reflected light of the lamp is introduced from a surface other than the front and back surfaces of the light guide, and this is reflected from a light guide surface, which is one surface of the front and back surfaces. I try to take it out. However, simply combining a lamp and a light guide results in the highest brightness near the lamp, and the brightness decreases rapidly away from the lamp, so that uniform brightness cannot be obtained on the light guide surface. Problems arise. Therefore,
Conventionally, the following two countermeasures have been proposed as countermeasures against this problem.

That is, as a first countermeasure, as shown in FIG. 6A, it has been proposed to dispose the filter 7 on the light extraction surface 21. As shown in FIG. 6B, the filter 7 is set so that the transmittance (indicated by a broken line) decreases as the distance from the lamp 1 decreases, and the filter 7 has a high luminance (indicated by a solid line). The more the transmittance is reduced, the more uniform brightness is to be obtained as a whole. However, in this countermeasure method, the luminance is made uniform by dimming the high luminance part.
There is a problem that the use efficiency of the emitted light of the lamp 1 is low.

Therefore, as a second countermeasure, as shown in FIG. 7 (a), the diffuse reflectance of the light diffusing surface on the opposite side of the light guide surface 21 of the light guide 2 is changed depending on the location. It is. That is, the diffuse reflectance is reduced in a portion close to the lamp 1, and the diffuse reflectance is increased as the distance from the lamp 1 increases.
Specifically, a point-like reflecting portion is provided on the light diffusing surface of the light guide 2.
23 (a hatched portion in FIG. 7 (a)) are formed, and as shown in FIG.
The distribution density is increased, and the portion without the reflection portion 23 is made to have an uneven surface, or is coated with a material having a different refractive index to perform an absorptive treatment. In this configuration, when the distance from the lamp 1 is about five times the plate thickness of the light guide 2, the difference in the density of the reflecting portion 23 between the vicinity of the lamp 1 and the portion far from the lamp 1 increases, There is a problem that the distribution density of the neighboring reflecting portions 23 becomes very small, causing uneven brightness. In an extreme case, a portion having high brightness appears in a star shape. This phenomenon becomes more remarkable as the thickness of the light guide 2 becomes smaller.

[Object of the Invention] The present invention has been made in view of the above points, and an object of the present invention is to provide a planar lighting device in which the luminance of a light emitting surface is sufficiently uniform. .

[Disclosure of the Invention] (Constitution) The planar lighting device according to the present invention includes a lamp serving as a light source,
A light guide formed of a transparent material in a plate shape, the radiation of the lamp is introduced from a surface other than the front and back, and one surface of the front and back becomes a light guide surface and a light guide surface on the opposite side of the light guide surface is provided with a light guide. The light guiding surface is formed so as to be smoothly formed and totally reflects all of the luminous flux of the light emitted from the lamp that is not reflected by the light diffusing surface, and the light diffusing surface is formed with a large number of reflecting portions that perform diffuse reflection. It is configured such that the higher the combined distribution intensity of the direct light from the lamp and the totally reflected light on the light output surface on the light diffusion surface, the lower the distribution density of the reflective portion becomes, and the light output surface is The lamp is formed so that the direct light from the lamp is totally reflected, and the distribution density of the reflection part on the light diffusion surface is set so as to be inversely proportional to the light intensity on the light diffusion surface. After being reflected In which the luminance of the light emitting surface is set to be substantially uniform.

(Example) As shown in FIG. 1, a lamp 1 serving as a light source and a plate-shaped light guide 2 are housed in a box 10. Lamp 1
, A straight tube fluorescent lamp is used, and is disposed to face one side surface of the light guide 2. The light guide 2 is formed of a transparent material such as glass or acrylic. One surface of the front and back surfaces (the upper surface in FIG. 1B) is a light guiding surface 21 and the other surface is a light diffusing surface 22. The light exit surface 21
It is a smooth convex curved surface, and is set so that the distance to the light diffusing surface 22 is maximum at the intermediate portion and the distance to the light diffusing surface 22 is minimum at the position farthest from the lamp 1. On the other hand, as shown in FIG. 2, the light diffusing surface 22 has a large number of reflecting portions 23 substantially parallel to the longitudinal direction of the lamp 1, and each reflecting portion 23 performs diffuse reflection by printing or the like. Is formed in close contact with the light diffusion surface 22. Further, between the adjacent reflection portions 23, a planar transmission portion 24 is formed. Here, as shown in FIG. 2 (b), the distribution density of the reflection portion 23 changes according to the distance from the lamp 1, and the distribution density is in the middle portion up to the position farthest from the lamp 1. There is a local maximum, and the other parts monotonically increase.

The positional relationship between the lamp 1 and the light guide 2 is as follows.
Of the emitted light is introduced into the light guide 2 and the light diffusing surface 22
The light emitted from the lamp 1 is not reflected at least once by the light diffusing surface 22.
It cannot be taken out from 21.

One surface of the box 10 and the light exit surface 21 of the light guide 2
A diffuser plate 3 that performs diffuse transmission and diffuse reflection is disposed at a position facing the light-receiving surface. On the other hand, a surface facing the light-diffusing surface 22 on the inner peripheral surface of the box 10 is a reflection surface 4. ing.
The diffuser plate 3 is arranged separately from the light guide 2, but may be arranged in close contact. The reflection surface 4 is a regular reflection surface that is a metal surface or a diffuse reflection surface formed by painting or the like, and reflects a light beam transmitted through the transmission part 24 of the light diffusion surface 22 of the light guide 2.

With the above configuration, the luminous flux emitted from the lamp 1 is
A part of the light is totally reflected by the light exit surface 21 and guided to a part remote from the lamp 1. By the way, considering the radiated light from the lamp 1, as shown in FIG. 3 (a), the distribution of the luminous flux directly irradiated from the lamp 1 to the light diffusing surface 22 is inversely proportional to the square of the distance. As shown in FIG. 6B, the value decreases monotonously. Further, as shown in FIG. 4 (a), the distribution of the luminous flux totally reflected from the lamp 1 on the light guiding surface 21 and reaching the light diffusing surface 22 is, as shown in FIG. It rises at a site separated by a predetermined distance, and gradually decreases from there. Therefore, as shown in FIG. 5, the light intensity distribution on the light diffusing surface 22 has a tendency to gradually decrease, temporarily reach a minimum, then reach a maximum and then decrease again. Here, as described above, on the light diffusing surface 22, the distribution density of the reflecting portion 23 gradually increases from the end on the lamp 1 side of the light guide 2 toward the other end, and reaches a maximum and a minimum. This distribution is set to increase again, so this distribution
If the light intensity at 22 is set to be in an inverse proportional relationship, the luminance distribution on the light output surface 21 becomes substantially uniform.

Further, in the present embodiment, the presence of the diffusion plate 3 and the reflection surface 4 allows the light of the portion corresponding to the transmission portion 24 of the light diffusion surface 22 to be reflected on the reflection surface 4 and used. This further enhances the light use efficiency.

As described above, by changing the distribution density of the reflecting portions 23 formed on the light guide 2, there is an advantage that the entire luminance distribution can be made uniform.
In addition, since the light guide 2 is sandwiched between the diffusion plate 3 and the reflection surface 4, unevenness in brightness due to the presence of the reflection portion 23 and the transmission portion 24 is reduced, so that the effect of uniformizing brightness is high. Since the pattern of the portion 23 is not conspicuous, and all the direct light from the lamp 1 is reflected on the light output surface, the radiated light from the lamp 1 can reach a part remote from the lamp 1. It has the advantage that. Also, since no dimming filter is used,
There is an advantage that the use efficiency of the emitted light of the lamp 1 is increased. Further, a reflection unit 23 for performing diffuse reflection and a transmission unit 24
The reflection surface 4 and the diffusion plate 3 correspond to each other to achieve uniform luminance in three stages, so that the effect of uniformizing luminance is high,
In addition, there is an advantage that high efficiency can be obtained.

[Effects of the Invention] As described above, the present invention provides a lamp serving as a light source, a plate formed of a transparent material, and radiated light of the lamp is introduced from a surface other than the front and back surfaces, and one surface of the front and back surfaces serves as a light extraction surface and a light extraction surface. The light guide surface of the light guide is formed smoothly, and the light guide surface of the light guide is formed so as to totally reflect all of the luminous flux of the light emitted from the lamp that is not reflected by the light diffusion surface. The light diffusion surface is formed with a large number of reflection portions that perform diffuse reflection, and the reflection portion increases as the combined distribution intensity of the direct light from the lamp and the total reflection light on the light extraction surface on the light diffusion surface increases. The distribution density of the light guide is set to be low, and the direct light from the lamp is totally reflected on the light guide surface, and in forming the reflection portion and the transmission portion on the light diffusion surface of the light guide, From the ramp The higher the combined distribution intensity of the direct light and the total reflection light on the light output surface on the light diffusion surface, the lower the distribution density of the reflection part is, so that the uniformity of the brightness on the light emission surface can be achieved. Have. In addition, since the luminance is made uniform by reflection and diffusion, and no dimming means is used, there is an advantage that the efficiency of using the emitted light of the lamp is high.

[Brief description of the drawings]

1 (a) and 1 (b) are a plan view and a sectional view, respectively, showing an embodiment of the present invention, and FIGS. 2 (a), 2 (b) show patterns of a reflection portion formed on the light diffusion surface, respectively. FIG. 3 is a plan view showing the distribution density, FIG. 3 is an explanatory view showing the direct light from the lamp on the light diffusing surface of the above, and FIG. FIGS. 5 and 5 are operation explanatory diagrams showing the combined light intensity on the light diffusing surface of the above, FIGS. 6 (a) and 6 (b) are schematic configuration diagrams and operation explanatory diagrams respectively showing a conventional example, and FIG. 7 (a). (B) is a schematic configuration diagram showing another conventional example, and is an explanatory diagram showing the distribution density of the reflection portion. 1 is a lamp, 2 is a light guide, 21 is a light exit surface, 22 is a light diffusion surface, 23 is a reflection part, and 24 is a transmission part.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-109003 (JP, A) JP-A-61-36911 (JP, U) JP-A-62-28306 (JP, U) JP-A-61-28306 14411 (JP, U)

Claims (1)

(57) [Claims] 1. A lamp as a light source, and a plate formed of a transparent material, radiation emitted from the lamp is introduced from a surface other than the front and back surfaces, one surface of the front and back surfaces becomes a light extraction surface, and a side opposite to the light extraction surface is a light diffusion surface. The light guide surface of the light guide is formed so as to be smoothly formed and totally reflect all of the luminous flux of the radiated light of the lamp that is not reflected by the light diffusion surface, and the light diffusion surface is A large number of reflective portions that perform diffuse reflection are formed, and the distribution density of the reflective portions decreases as the combined distribution intensity of the direct light from the lamp and the totally reflected light on the light output surface on the light diffusion surface increases. A planar lighting device characterized by being set.