JP2603649C - - 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. This filter 7 is shown in FIG.
As shown in (2), the transmittance (indicated by a broken line) is set to decrease as the distance from the lamp 1 decreases, and in this countermeasure that the transmittance decreases as the luminance (indicated by a solid line) increases. Since the luminance is made uniform by dimming the high-luminance part, there arises a problem that the use efficiency of 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 density of the reflecting portion 23 between the vicinity of the lamp 1 and a portion distant from the lamp 1 increases, and A problem arises in that the distribution density of the neighboring reflection portions 23 becomes extremely 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 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. And a light guide having a light diffusing surface on the opposite side of the light guiding surface, and the light guiding surface of the light guide is formed of all of the luminous flux of the emitted light of the lamp that is not reflected by the light diffusing surface. In a certain distance range from the lamp so as to totally reflect the light, the distance from the lamp increases as the distance from the lamp increases, and the light diffusion surface is formed with a large number of reflection parts that perform diffuse reflection, and The distribution density of the reflecting portion is set lower as the combined distribution intensity of the direct light and the total reflection light on the light output surface on the light diffusion surface becomes higher. Is totally reflected And the distribution density of the reflection portion on the light diffusion surface is set so as to be inversely proportional to the intensity of light on the light diffusion surface. The brightness is made 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. 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 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 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, 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 beam emitted from the lamp 1 is totally reflected by the light output surface 21 and guided to a part distant from the lamp 1. By the way, considering the radiated light from the lamp 1, as shown in FIG. 3A, the distribution of the luminous flux directly radiated 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 distributed from the lamp 1 as shown in FIG. 4 (b). 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 portions 23 is set so as to gradually increase from the end on the lamp 1 side of the light guide 2 toward the other end, reach a maximum and a minimum, and then increase again. Therefore, if this distribution is set so as to be in inverse proportion to the light intensity on the light diffusion surface 22, the luminance distribution on the light extraction surface 21 becomes substantially uniform. Furthermore, 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 by the reflection surface 4 and used. This further enhances the light use efficiency. As described above, there is an advantage that the entire luminance distribution can be made uniform by changing the distribution density of the reflecting portions 23 formed on the light guide 2. 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. Since the pattern of the portion 23 is not conspicuous and all the direct light from the lamp 1 is reflected on the light exit surface, the radiated light from the lamp 1 can reach a part remote from the lamp 1. It has the advantage that. 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, the reflection unit 23 that performs diffuse reflection
In addition, since the luminance is made uniform in three stages by the reflection surface 4 corresponding to the transmission portion 24 and the diffusion plate 3, there is an advantage that the effect of uniforming the luminance is high and high efficiency is 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 of the front and back surfaces serves as a light extraction surface and a light extraction surface. And a light guide having a light diffusing surface on the opposite side of the light guide, and the light guide surface of the light guide is formed so as to totally reflect all the luminous flux of the radiated light of the lamp that is not reflected by the light diffusing surface. In a certain distance range from the lamp, the distance from the lamp increases as the distance from the lamp increases, and the light diffusion surface is formed with a large number of reflection parts that perform diffuse reflection. The distribution density of the reflecting part is set to be lower as the combined distribution intensity on the light diffusion surface with the total reflection light at the surface is higher, and the direct light from the lamp is totally reflected at the light output surface West, In addition, when forming the reflecting portion and the transmitting portion on the light diffusing surface of the light guide, the distribution of the reflecting portion increases as the combined distribution intensity on the light diffusing surface of the direct light from the lamp and the total reflection light on the light guiding surface increases Since the density is reduced, there is an advantage that the luminance on the light emitting 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 an embodiment of the present invention, and FIGS.
FIGS. 3A and 3B are a plan view showing a pattern of a reflecting portion formed on the light diffusion surface and an explanatory diagram showing a distribution density, respectively. FIG. 3 is a diagram showing direct light from a lamp on the light diffusion surface. FIG. 4 is an operation explanatory diagram showing direct light from a lamp on the light extraction surface of the above, FIG. 5 is an operation explanatory diagram showing combined light intensity on the light diffusing surface of the above, and FIG. 6 (a). (B) is a schematic configuration diagram and operation explanatory diagram showing a conventional example, and FIG.
FIGS. 1A and 1B are a schematic configuration diagram showing another conventional example and an explanatory diagram showing a distribution density of a 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.

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 that is a light diffusing surface, and the light guide surface of the light guide is formed smoothly and is fixed from the lamp so as to totally reflect all of the luminous flux of the radiated light of the lamp that is not reflected by the light diffusing surface. In the distance range of
The light diffusing surface is formed with a large number of reflective portions that perform diffuse reflection, and is formed on the light diffusing surface between direct light from the lamp and total reflected light on the light guiding surface. A planar lighting device characterized in that the distribution density of the reflection portion is set to be lower as the combined distribution intensity is higher.