JP2603650C - - 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 radiates light from a lamp from a surface other than the front and back of the light guide, and transmits the light from a light guide surface, which is one surface of the front and back. 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, the following two countermeasures have been proposed as countermeasures against this problem. That is, as a first countermeasure, as shown in FIG. 6 (a), it is proposed that the filter 7 is provided opposite to the light extraction surface 21. As shown in FIG. 6 (b), the filter 7 is set so that the transmittance (dashed line) decreases as the distance from the lamp 1 decreases, and the transmittance increases as the luminance (solid line) increases. By lowering the luminance, it is intended to obtain a uniform luminance as a whole. However, in this countermeasure, since the luminance is made uniform by reducing the intensity of the high-luminance portion, there arises a problem that the efficiency of using the radiated 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 large number of dot-like reflecting portions 23 (hatched portions in FIG. 7A) are formed on the light diffusing surface of the light guide 2 and separated from the lamp 1 as shown in FIG. 7B. The higher the distribution density of the reflecting portion 23 is, the more the surface without the reflecting 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 distribution density of the reflecting portion 23 between the vicinity of the lamp 1 and the portion far from the lamp 1 increases, and There is a problem that uneven brightness occurs due to the portion 23, and a wide gap is formed between the reflecting portions 23 in the vicinity of the lamp, so that a portion having high brightness appears in a star shape. This phenomenon becomes more remarkable as the thickness of the light guide 2 decreases. [Object of the Invention] The present invention has been made in view of the above points, and the object thereof is as follows.
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] (Configuration) A planar lighting device according to the present invention includes a lamp serving as a light source, and a plate formed of a transparent material, in which radiated light of the lamp is introduced from a surface other than the front and back, and one surface of the front and back is a light output surface. A light guide having a light diffusion surface on the opposite side of the light guide surface, a diffusion plate opposed to the light guide surface of the light guide to perform diffuse reflection and diffusion transmission, and a reflection provided opposite to the light diffusion surface of the light guide. The light guide surface of the light guide is far from the lamp within a certain distance range from the lamp so that the light guide surface of the light guide is formed smoothly and totally reflects all of the luminous flux of the radiated light of the lamp that is not reflected by the light diffusing surface. The light diffusion surface is inclined so that the distance from the light diffusion surface increases, and the light diffusion surface is formed with a large number of reflection portions that perform diffuse reflection.The greater the distance from the lamp, the greater the distribution density of the reflection portions is set. ,
The reflection surface is configured to reflect a light beam transmitted through a transmission portion between the reflection portions formed on the light diffusion surface of the light guide. In addition to making the brightness uniform, the use efficiency of the radiated light of the lamp is enhanced by not using the means for dimming. Embodiment 1 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. As the lamp 1, a straight tube fluorescent lamp is used, and is disposed to face one side 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 guiding surface 21 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. ing. On the other hand, as shown by the hatched portion in FIG.
Has a large number of reflecting portions 23 substantially parallel to the longitudinal direction, and each reflecting portion 23 is formed in close contact with the light diffusing surface 22 so as to perform diffuse reflection by printing or the like. Further, between the adjacent reflection portions 23, a planar transmission portion 24 is formed. Here, the reflection unit 23
The width is smaller so as to be closer to the lamp 1, and the width of the transmission portion 24 is wider. The positional relationship between the lamp 1 and the light guide 2 is set so that all of the luminous flux of the radiated light of the lamp 1 which is introduced into the light guide 2 and not reflected by the light diffusing surface 22 is totally reflected. Thus, the radiated light from the lamp 1 cannot be taken out of the light guide surface 21 unless reflected by the light diffusion surface 22 at least once. On one surface of the box body 10 and at a position facing the light guide surface 21 of the light guide 2, a diffusion plate 3 that performs diffuse transmission and reflection is provided. The surface facing the light diffusion surface 22 is the reflection surface 4. Diffusing plate 3
Are arranged apart from the light guide 2, but may be arranged in close contact. Reflective surface 4
Is a specular reflection surface which is a metal surface or a diffuse reflection surface formed by painting or the like, and reflects a light beam transmitted through the transmission portion 24 of the light diffusion surface 22 of the light guide 2. With the configuration described above, a part of the light flux emitted from the lamp 1 is totally reflected by the light guide surface 21 and guided to a part distant from the lamp 1. Since the distribution density of the transmission portions 24 is high, the transmission portions 2
4, the radiated light of the lamp 1 is guided to a part remote from the lamp 1. On the other hand, since the distribution density of the reflecting portions 23 on the light diffusing surface 22 is small in the vicinity of the lamp 1, the diffuse reflection is relatively small. As a result, the amount of light extracted from the light extracting surface 21 is substantially uniform. Become. Here, if the diffusion plate 3 and the reflection surface 4 do not exist, as shown in FIG.
The configuration is equivalent to the second countermeasure method described in the section of the background art, and as shown in FIG. 3B, the portion of the light diffusing surface 22 corresponding to the reflection portion 23 has a high luminance, and Part 2
The portion corresponding to No. 4 has low brightness, causing uneven brightness. In practice, however, a part of the light flux is diffusely reflected by the diffuser plate 3 and has a brightness distribution as shown in FIG. Further, of the reflected light, the light flux reflected so as to be incident on the transmission portion 24 of the light diffusion surface 22 of the light guide 2 at an incident angle smaller than the critical angle is transmitted through the light guide 2 and is reflected on the reflection surface. 4 will be reflected, and therefore the brightness in this part will increase. As a result, in the portion corresponding to the transmitting portion 24, the difference between the luminance of the reflecting portion 23 and the luminance of the reflecting portion 23 is reduced by the reflection between the diffusion plate 3 and the reflecting surface 4.
Furthermore, since the light finally passes through the diffusion plate 3 and is extracted to the outside of the box 10, the luminance distribution is made uniform as shown in FIG. 3 (d). As described above, by changing the distribution density of the reflecting portions 23 formed on the light guide 2, the entire luminance distribution is roughly made uniform, and the light guide 2 is sandwiched between the diffusion plate 3 and the reflection surface 4. As a result, uneven brightness due to the presence of the reflective portion 23 and the transmissive portion 24 is mitigated. Therefore, the effect of uniformizing the brightness is high. Even when the thickness is reduced, the pattern of the reflective portion 23 is not conspicuous, and the pattern of the reflective portion 23 is fine. This has the advantage that the thickness can be reduced without having to do so. Further, since no light-attenuating filter is used, there is an advantage that the efficiency of using the emitted light of the lamp 1 is increased. Further, since the luminance is made uniform in three stages by the reflecting portion 23 that performs diffuse reflection, the reflecting surface 4 corresponding to the transmitting portion 24, and the diffusion plate 3, the effect of making the luminance uniform is high,
In addition, there is an advantage that high efficiency can be obtained. In the above-described configuration, when direct light from the lamp 1 is incident on the diffusion plate 3 to increase the luminance near the lamp 1, as shown in FIG. 5 may be arranged in an appropriate place. Embodiment 2 In this embodiment, as shown in FIG. 4, the lamp 1 is a point light source such as an incandescent lamp,
It has a circular light emitting surface centered on the lamp 1. That is, the light guide 2 is disposed around the lamp 1 as a center, and the pattern of the reflecting portion 23 on the light diffusing surface 22 is concentric as shown by oblique lines in FIG. 4 (b). I have. Also, since the lamp 1 is located at the center of the light emitting surface, the lamp 1
The light shielding plate 6 is provided at a portion corresponding to the above, so that the transmitted light of this portion is not used, or a member that performs diffuse reflection and diffuse transmission with characteristics different from those of the diffusion plate 3 is provided at this portion. , To make the luminance uniform. The other configuration is the same as that of the first embodiment, and the description is omitted. (Embodiment 3) In the present embodiment, two lamps 1 are provided, and the configuration of Embodiment 1 is combined to make the lamp 1 symmetrical. That is, according to this configuration, it is possible to obtain a planar lighting device having the same luminance as that of the first embodiment and a light emitting surface having twice the area.
The other configuration is the same as that of the first embodiment, and the description is omitted. [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 of the front and back surfaces serves as a light extraction surface and a light extraction surface. A light guide having a light diffusing surface on the opposite side of the light guide, a diffuser plate opposed to the light guide surface of the light guide to perform diffuse reflection and diffusion transmission, and a reflective surface opposed to the light diffusing surface of the light guide, The light guide surface of the light guide has a light diffusion surface as it is farther from the lamp within a certain distance from the lamp so that the light guide surface is formed smoothly and totally reflects all the light flux not reflected by the light diffusion surface out of the lamp radiation. The light-diffusing surface is formed with a large number of reflecting portions that perform diffuse reflection, and the longer the distance from the lamp, the greater the distribution density of the reflecting portions is set. The light guide is set so as to reflect a light beam transmitted through the transmission portion between the reflection portions formed on the light diffusion surface of the light guide, and the reflection portion and the transmission portion are appropriately formed on the light diffusion surface of the light guide. In addition, since the reflection and the diffusion are repeated by sandwiching the light guide between the diffusion plate and the reflection surface, there is an advantage that the luminance on the light emission surface can be made uniform. 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 FIGS. 1 (a) and 1 (b) are a plan view and a sectional view, respectively, showing a first embodiment of the present invention, and FIGS.
FIG. 3 is a plan view showing a pattern of a reflecting portion formed on the light diffusing surface of the above, FIG. 3 is an operation explanatory view of the above, and FIGS. 4 (a) and (b) are cross-sectional views of Example 2 of the present invention, respectively. And FIG. 5 is a plan view showing a pattern of a reflection portion formed on the light diffusing surface, FIG. 5 is a cross-sectional view showing a third embodiment of the present invention, and FIGS. FIGS. 7 (a) and 7 (b) are a schematic configuration diagram showing another conventional example and an explanatory diagram showing the distribution density of the reflecting portion, respectively. 1 is a lamp, 2 is a light guide, 3 is a diffusion plate, 4 is a reflection surface, 21 is a light extraction surface,
22 is a light diffusing surface, 23 is a reflecting part, and 24 is a transmitting part.

Claims (1)

(1) A lamp serving 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 the opposite side surface of the light extraction surface is formed. A light guide serving as a light diffusion surface, a diffusion plate opposed to a light guide surface of the light guide and configured to perform diffuse reflection and diffuse transmission, and a reflection surface opposed to the light diffusion surface of the light guide. The exit surface should be designed so that all the luminous flux of the radiated light of the lamp not reflected by the light diffusing surface is totally reflected .
Within a certain distance range, the farther from the lamp, the greater the distance to the light diffusing surface.
The light diffusing surface is formed with a large number of reflecting portions that perform diffuse reflection, and the distribution density of the reflecting portions is set to increase as the distance from the lamp increases, and the reflecting surface is formed on the light diffusing surface of the light guide. A planar lighting device characterized in that it is set so as to reflect a light beam transmitted through a transmitting portion between the reflecting portions.