JP2001272678A - Planar light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar light emitting device which can prevent irregular luminance on the light emitting face. SOLUTION: The reflector 2 is formed as divided for each light source 1 facing the light emitting face 3 and the light source 1 is disposed in an off-set position from the focal point of the paraboloid of the reflector 2 to generate uniform surface luminance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat light emitting device used as a backlight for a liquid crystal or the like.

[0002]

2. Description of the Related Art As a backlight of a liquid crystal or the like, for example,
An illuminating device having a plurality of light-emitting portions that can be selectively turned on and off, as disclosed in JP-A-64-82019;
An illumination scanning circuit for scanning and flashing the light emitting portion one after another in accordance with the timing of driving the image scanning electrode of the liquid crystal display, wherein the illumination scanning circuit comprises an image scanning electrode in which the light emitting portion is within each illumination range. Are turned on immediately after all are selected, and are turned off after a predetermined time, so that only the moments with a high contrast ratio remain as afterimages for the viewer, and appear as a clear image with a good contrast ratio. Has been proposed.

[0003]

However, if a higher speed moving image is demanded for such a conventional technique,
At this conventional level, there remains a problem with the contrast ratio.
On the other hand, this backlight has a problem that it cannot be operated at 60 Hertz (Hz) or less because a plurality of light sources are turned on at the same time and the light emitting surface is shared.

[0004] In view of the above, the backlight reflector is divided and sequentially turned on, so that the backlight lighting time is shortened without changing the response speed of the liquid crystal, and the backlight is divided and lighted at 60 Hz or less. However, as shown in FIG. 4, when the position of the light source 1 is set to the focal point of the paraboloid of the reflector 2 as shown in FIG. The light emission luminance of the portion 3a of the light emitting surface 3 corresponding to the position directly above the light source 1, as indicated by reference numeral 4,
Get higher. That is, in the light emitting surface 3, the portion 3 a directly above the light source 1 is bright, and the brightness 4 decreases as the distance from the portion 3 a increases, so that the light emitting surface 3 has uneven brightness. do not become.

The present invention has been made by paying attention to such a conventional technique, and provides a flat light emitting device capable of preventing luminance unevenness on a light emitting surface.

[0006]

According to a first aspect of the present invention, a light emitting surface is formed by diffusing or mirroring a light source for each light source, and is shifted from the focal point of the paraboloid of the reflector. The light source was arranged at a position where the luminance was uniform.

According to the first aspect of the present invention, the light emitted from the light emitting surface can be made uniform by lowering the brightness of the portion of the diffuser or mirror reflector just above the light source.

According to a second aspect of the present invention, the light source is disposed at a bottom of the reflector.

According to the second aspect of the present invention, the light source can be supported without being distorted, and partial luminance unevenness of the reflector can be surely eliminated. Further, a holder for fixing the light source is not required, and the cost can be reduced.

According to a third aspect of the present invention, at least a part of the light source is covered by a transparent cap.

According to the third aspect of the present invention, it is possible to compensate for a decrease in luminance due to a decrease in the tube wall temperature of the light source due to duty driving. Furthermore, there is no light amount loss due to the means for supporting the light source.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIGS.

Reference numeral 1 denotes a light source, which is a thin cold-cathode tube having a diameter of 2.4 mm, and is disposed on each of the divided reflectors 2. The position of the light source 1 in the reflector 2 is shifted from the focus of the paraboloid of the reflector 2 and is a position where the surface luminance is uniform, and is supported by the transparent cap 7 on the bottom surface 2a of the reflector 2. .

Reference numeral 5 denotes a case supporting the reflector 2, and the case 5 is provided with a diffusion plate 3 serving as a light emitting surface. The diffusion plate 3 is a white plate material that scatters light passing therethrough. Reference numeral 6 denotes an inverter that controls on / off of the light source 1.

Next, the operation of this embodiment will be described. As shown in FIG. 2, the light from the light source 1 lowers the luminance 4 of the portion 3a immediately above the light source 1 of the reflector 2 so that the light emitted from the diffusion plate 3 as the light emitting surface can be made uniform.

Further, by disposing the light source 1 on the bottom 2a of the reflector 2, the light source 1 can be supported without being distorted, and the partial brightness unevenness of the reflector 2 can be surely reduced. Can be eliminated. Further, a holder for fixing the light source 1 is not required, and the cost can be reduced.

Further, since at least a part of the light source 1 is covered by the transparent cap 7, it is possible to compensate for a decrease in luminance due to a decrease in the tube wall temperature of the light source 1 due to duty driving. Furthermore, since the cap 7 is transparent,
There is no light amount loss due to the means for supporting the light source 1.

In addition, since the light from the light source 1 is diffused by the diffusion plate 3, the light source 1 cannot be seen from the outside, and the luminance on the light emitting surface can be made uniform.

[0019]

According to the first aspect of the present invention, it is possible to make the light emitted from the light emitting surface uniform by lowering the brightness of the portion of the reflector immediately above the light source.

According to the second aspect of the present invention, the light source can be supported without being distorted, and partial luminance unevenness of the reflector can be surely eliminated. Further, a holder for fixing the light source is not required, and the cost can be reduced.

According to the third aspect of the invention, it is possible to compensate for a decrease in luminance due to a decrease in the tube wall temperature of the light source due to the duty driving. Furthermore, there is no light amount loss due to the means for supporting the light source.

[Brief description of the drawings]

FIG. 1 is a partially sectional perspective view showing a flat light emitting device of the present invention.

FIG. 2 is a sectional view of FIG.

FIG. 3 is a perspective view of a main part of FIG. 2;

FIG. 4 is a sectional view corresponding to FIG. 2 of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Reflector 2a Bottom part of reflector 3 Diffusion plate which is light emitting surface 3a Portion immediately above light source 4 Luminance 7 Cap

Claims (3)

[Claims] 1. A light source, wherein a light source is formed by dividing a light source by a diffuser or a specular reflector, and displaced from a focal point of a parabolic surface of the reflector so as to have a uniform surface luminance. A flat light emitting device characterized by the above-mentioned. 2. The flat light emitting device according to claim 1, wherein the light source is disposed on a bottom of the reflector. 3. The flat light emitting device according to claim 2, wherein at least a part of the light source is covered by a transparent cap.