JP2554180Y2 - Surface light source device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface light source device using a light guide used for a backlight or the like of a liquid crystal device.

[Prior Art] In a conventional surface light source device using a light guide, as shown in FIGS. 4 and 5, a linear light source 1 such as a cold-cathode tube and an incident end face 2a are brought close to the light source 1. Light guide 2 composed of a transparent body arranged
And a diffusion plate 3 disposed on the surface of the light guide 2 and a reflection surface 4 formed on the back surface of the light guide 2. Light from the light source 1 enters the light guide 2 from the incident end face 2 a. The light enters and is transmitted from the incident end face 2a side in the opposite direction while being sequentially reflected by the upper and lower surfaces. A part of the light transmitted in the light guide 2 in this manner exits from the surface of the light guide 2 and passes through the diffusion plate 3 to become diffused light. The diffused light from the diffuser plate 3 is bright near the incident end face 2a and decreases in brightness and becomes darker as the distance from the incident end face 2a increases. Fifth to eliminate the disadvantage
As shown in the figure, a pattern near the incident end face 2a is sparse in area and becomes denser as the distance from the incident end face 2a increases.
The brightness of the diffused light from the diffuser plate 3 is made uniform by a method such as milky white printing.

[Problem to be Solved by the Invention] In the surface light source device described above, the size of the light emitting surface of the diffusion plate 3 (the length of the incident end face 2a) and the total length of the light source 1 must be the same due to space restrictions. Sometimes. In such a case, due to the influence of the electrode portions 1a at both ends of the light source 1, there is a disadvantage that the luminance near the both ends of the incident end face 2a (near the reference numeral E in FIG. 5) is reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface light source device in which the entire surface of a diffusion plate including the above-described portion has uniform luminance.

[Means for Solving the Problems] The surface light source device of the present invention comprises a linear light source such as a cold cathode tube having electrodes at both ends, a light guide having an incident end face arranged close to the light source, and a light guide. And a reflecting surface provided on the back surface of the light guide, the length of the incident end face of the light guide being substantially equal to the entire length of the light source, and the back surface of the light guide. In the entire region of the back surface, the central portion has the lowest area ratio in the direction parallel to the longitudinal direction of the light source, and the area ratio increases toward both end portions. A pattern having a diffusing effect, such as a milky white print pattern, is provided so that the area ratio increases from the side toward the end face opposite to the incident end face.

In the lighting device of the present invention, the pattern having a diffusing action provided on the back surface of the light guide is formed as described above, so that in the above-described conventional lighting device, the luminance decreases as the distance from the incident end surface decreases. In addition, in the direction parallel to the longitudinal direction of the light source, in the range from the incident end surface to the surface facing the incident end surface, a difference in luminance between the vicinity of the center and the vicinity of both ends is caused by the above-described pattern. With this arrangement, the luminance of the light-emitting surface on the light guide side, that is, the surface on the diffusion plate was made uniform.

The pattern having a diffusion effect used in the illumination device of the present invention is obtained by changing the ratio of the area by arranging a large number of small regions having a diffusion effect whose area gradually changes at uniform intervals. Alternatively, the ratio of the area of the pattern having the diffusion effect may be changed by arranging a large number of small regions having the diffusion effect, each having a uniform area, while gradually changing the interval between them.

Next, an embodiment of the surface light source device of the present invention will be described with reference to the drawings.

1 and 2 show a first embodiment of the present invention. FIG. 1 is a sectional view, and FIG. 2 shows a pattern provided on the back surface of a light guide.

This embodiment includes a linear light source 1, a light guide 2, a diffusion plate 3, and a reflection surface 4. The light guide 2 is provided with a pattern 5 having a diffusing action, such as a milky white print pattern as shown in FIG. In other words, the spot-shaped diffused portion 5 of the portion indicated by reference numeral A in FIG. 2, which is the central portion on the side of the incident end face 2a of the light guide 2, has the smallest area, and then to the portions indicated by reference numeral B on both sides. The area is gradually increasing. Also, the area is gradually increased from the portion A to the portion indicated by the reference numeral C. Further, the area gradually increases from part C to both sides indicated by reference numeral D. That is, the area of the spot A, which is the central part on the side of the incident end face 2a, has the smallest area of the spot, and the area gradually increases in any direction as the spot becomes farther from the spot, and the spot of the spot D is the largest.

As described above, in the pattern used in this embodiment, the area ratio of the region having the diffusion action is the lowest at the central portion A on the side of the incident end face 2a, and the area ratio increases as the distance from the area increases. It is configured to be. The portion D farthest from A has the highest area ratio.

In Example 1 having such a pattern, in the portion A where the amount of incident light is large, the amount of diffused light due to the pattern is small, so that the transmission of light by total reflection is large, and Is suppressed, and as the distance increases, the diffusion effect of the pattern increases, and the amount of emitted light increases. As a result, the amount of light passing through the diffusion plate 3 becomes uniform, resulting in a uniform luminance distribution.

FIG. 3 is a view showing a pattern provided on the back surface of the light guide 2 according to the second embodiment of the present invention. In the second embodiment, a spot-like diffusing portion having the same area is provided, and the interval between the spots is large at the portion A and the direction from the direction A to the direction C increases. It's going to be smaller as you go. As described above, the pattern is formed such that the ratio of the area of the region where the portion A performs the diffusion action is the lowest, and as the distance from the region increases, the ratio of the area gradually increases.

In the second embodiment, the pattern provided on the light guide 2 is configured as shown in FIG. 3 and has the same operation as the first embodiment, whereby a uniform luminance distribution can be obtained. It is a lighting device.

[Effect of the Invention] The surface light source device of the present invention has a light source length (including an electrode portion).
And the length of the incident end face of the light guide are almost the same length, so that the device can be small compared to the area of the light emitting surface, and the brightness can be uniform over the entire light emitting surface.

[Brief description of the drawings]

1 and 2 show a first embodiment of the present invention.
The figure shows the pattern of the second embodiment, and FIGS. 4 and 5 are views of a surface light source device using a conventional light guide. DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Light guide, 3 ... Diffusion plate, 4 ... Reflection plate, 5 ...
Diffusion pattern

Claims (3)

(57) [Scope of request for utility model registration] 1. A linear light source having electrode portions at both ends, a light guide having an incident end face disposed close to the light source, a diffusion plate provided on a surface of the light guide, and a back surface of the light guide. In the surface light source device comprising the reflection surface provided in the above, while making the length of the incident end face of the light guide substantially equal to the entire length of the light source, providing a pattern having a diffusing action on the back surface of the light guide, The pattern is arranged almost in parallel with the linear light source and the ratio of the area is the lowest in the direction parallel to the longitudinal direction of the light source in the entire region on the back surface of the light guide. The surface light source device is characterized in that the area ratio increases from the incident end face side to the end face opposite to the incident end face. 2. The method according to claim 1, wherein the ratio of the area of the pattern is changed by arranging a large number of small regions having a diffusion action, the area of which gradually changes, at uniform intervals. 1. Surface light source device. 3. The method according to claim 1, wherein the change of the ratio of the area of the pattern is performed by arranging small regions having the same diffusion area having the same diffusion function while gradually changing the interval between them. 1. Surface light source device.