JPH05150235A - Illumination device - Google Patents

Abstract

PURPOSE:To enhance transmissivity, to eliminate the irregularity of brightness by using a light diffusing plate whose diffusing property is low and to improve the utilizing efficiency of light. CONSTITUTION:The front part of a bar-like cold cathode fluorescent lamp 1 is covered with the light diffusing plate 6 and a reflecting mirror 7 is arranged at the back part of the lamp 1. The mirror 7 consists of a first curved surface 7a and a second curved surface 7b positioned at the central part of the first curved surface. Besides, the lamp 1 is positioned at the focus coordinate of the first curved surface 7a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illuminating device suitable as a back illuminator for a liquid crystal display device used in a personal computer device, a liquid crystal television device or the like.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, a lighting device of this type has a rod-shaped fluorescent lamp 1 and a light diffusion plate 2 covering the front thereof.
And a parabolic reflecting mirror 3 arranged behind the rod-shaped fluorescent lamp 1 are general. Here, as shown in FIG. 6, the wall thickness of the rod-shaped fluorescent lamp 1 is 0.5.
A fluorescent substance 5 having a uniform film thickness is applied to the inner surface of the glass tube 4 having a diameter of 25 mm.
The phosphor 5 is excited by the ultraviolet radiation of 4 nm to become visible light, and the light is emitted. However, above the thick portion of the glass tube 4, the light cannot proceed because it is limited by the critical angle on the inner surface of the glass tube 4.

FIG. 7 shows a path of light when the inner wall surface of the rod-shaped fluorescent lamp 1 is restricted by a critical angle. Soda glass generally used as a glass tube material for the rod-shaped fluorescent lamp 1 has a critical angle of about 45 °,
Light incident (emitted) at an angle larger than this is totally reflected. Therefore, the light emitted from the point a on the inner wall surface of the rod-shaped fluorescent lamp 1 is also limited by the critical angle (45 °) and can proceed only in the direction shown in FIG. 7. This is the same below the point a on the inner wall surface of the glass tube 4, and the light does not travel above the thick portion of the glass tube 4 as indicated by the broken line. In addition, in the parabolic reflector 3, the rod-shaped fluorescent lamp 1
It is designed to reflect the light emitted from the parallel diffused light to the light diffusing plate 2. This reflected light also hits the fluorescent substance 5 on the inner surface of the glass tube 4 of the rod-shaped fluorescent lamp 1, and the rod-shaped fluorescent lamp 1 Light does not travel above the thick part of.
As a result, the thick portion of the rod-shaped fluorescent lamp 1 becomes a substantially non-light emitting portion. Therefore, in the conventional lighting device, a light diffusing plate having high diffusivity is provided to make the luminance distribution uniform. The brightness distribution characteristic at that time is shown as a curve D in FIG.

[0004]

However, in the above-mentioned conventional configuration, since the parabolic reflector 3 is used, when the illumination device is made thin, the rod-shaped fluorescent lamp 1 is replaced by the light diffusion plate 2. When approaching, there is a problem in that the sharp decrease in brightness of the thick portion of the rod-shaped fluorescent lamp 1 is increased, and the uniformity of the brightness distribution is likely to deteriorate. Therefore, in order to make the luminance distribution uniform, a light diffusion plate having a low transmittance and a high diffusivity is used.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to eliminate uneven brightness by using a light diffusing plate having a high transmittance and a low diffusivity, thereby improving the light utilization efficiency. A lighting device that can be improved.

[0006]

According to another aspect of the present invention, there is provided an illuminating device comprising a linear light source, a light diffusing plate covering the front of the linear light source, and a reflecting mirror arranged behind the linear light source. The reflecting mirror is provided with a first curved surface and a second curved surface at the center of the first curved surface, and the linear light source is positioned at the focal point coordinates of the first curved surface.

[0007]

In this structure, when the linear light source is turned on, the light traveling to the first curved surface portion of the reflecting mirror is reflected as parallel light to the light diffusing plate as in the conventional example. Next, the light that has proceeded to the second curved surface is condensed on the tube wall of the linear light source and reflected as parallel light to the light diffusion plate. With this light, it is possible to prevent a sharp decrease in brightness on the upper surface of the thick portion of the linear light source where brightness unevenness is most noticeable.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an illuminating device which is an embodiment of the present invention. As shown in FIG. 1, the illumination device of the embodiment of the present invention includes a linear light source composed of a rod-shaped cold cathode fluorescent lamp 1 having an outer diameter of 4 mm, a light diffusing plate 6 covering the front of the linear light source, and a parabolic first light source.
The curved surface 7a and the arc-shaped second curved surface 7 at the center of the first curved surface
and a reflecting mirror 7 in which b is located. Here, in the embodiment of the present invention, the first curved surface 7a is defined by the following formula that is generally used as a design formula of a parabolic reflector, and the focal length f =
It was set to 2.031.

(X ² -4f) -f = Y (where (X, Y) is the coordinates of the reflecting mirror, and f is the focal length. The focal coordinates are (0,0).) The second curved surface 7b is (3.77, -0.2) on the first curved surface 7a.
6), (-3.77, -0.26) is an arc connecting two points. As the reflecting mirror 7, the one having the same reflectance as the reflecting mirror of the conventional example is used.

The operation of the illuminating device of the embodiment of the present invention constructed as above will be described below with reference to FIG.

First, when the rod-shaped cold cathode fluorescent lamp 1 is turned on, the light traveling to the first curved surface 7a of the reflecting mirror 7 is reflected as parallel light to the light diffusing plate 6 as in the conventional example. next,
The light that has proceeded to the second curved surface 7b is condensed on the tube wall of the cold cathode fluorescent lamp 1 and reflected as parallel light to the light diffusion plate 6. FIG. 3 shows the result of measuring the luminance distribution without using the light diffusing plate 6. In the figure, a curve A shows the case of the embodiment of the present invention, and a curve B shows the conventional example (without a light diffusion plate). From this, it can be seen that the sudden decrease in brightness on the upper surface of the thick portion of the cold cathode fluorescent lamp 1 is alleviated as compared with the conventional example. Therefore, the luminance distribution can be made uniform by using the light diffusing plate having a higher transmittance and a lower diffusivity than the conventional one because the decrease in the luminance is alleviated. The luminance uniformity in this example is 66.4.
%, And 66.1% in the conventional example.

FIG. 4 shows a curve C as a luminance distribution characteristic of the illuminating device to which the light diffusing plate is attached in the embodiment of the present invention.
It can be seen from FIG. 4 that according to the embodiment of the present invention, the luminance of the light diffusing plate surface is about twice as high as that of the conventional case, while the luminance uniformity is about the same with the same lamp input.

As described above, according to the embodiment of the present invention, the reflecting surface that causes reflection of the tube wall to the cold cathode fluorescent lamp 1 at the center of the parabolic first curved surface 7a of the reflecting mirror 7, that is, the second surface. By providing the curved surface 7b, it is possible to suppress a sharp decrease in brightness on the upper surface of the thick portion of the cold cathode fluorescent lamp 1, and to use a light diffusing plate having a transmittance that is about twice that of the conventional one to achieve a similar brightness uniformity. Obtainable. In other words, the light utilization efficiency is about 2
Can be doubled.

Although the first curved surface of the reflecting mirror is parabolic and the second curved surface is arcuate in the above embodiment, the curved shapes of the first curved surface and the second curved surface are different depending on the maximum allowable thickness of the lighting device. Any combination may be used. Further, in the above embodiment, the cold cathode fluorescent lamp is used as the linear light source, but a hot cathode fluorescent lamp, an electrodeless fluorescent lamp or the like may be used.

[0016]

As described above, according to the present invention, the line light source, the light diffusing plate covering the front of the line light source, and the reflecting mirror arranged behind the line light source are provided. A mirror is provided with a first curved surface and a second curved surface at the center of the first curved surface, and by positioning the linear light source at the focal point coordinates of the first curved surface, it is possible to sharply move above the thick portion of the linear light source. It is possible to suppress the decrease in brightness, and to make the brightness distribution uniform by using a light diffusion plate with higher transmittance and lower diffusivity than before, which is an excellent way to improve light utilization efficiency. It is possible to provide a lighting device having an effect.

[Brief description of drawings]

FIG. 1 is a sectional view of a lighting device according to an embodiment of the present invention.

FIG. 2 is an optical path diagram of a reflecting mirror portion in FIG.

FIG. 3 is a luminance distribution characteristic of the embodiment of the present invention (without a light diffusion plate)
Figure showing comparison with that of the conventional example

FIG. 4 is a luminance distribution characteristic of the embodiment of the present invention (with a light diffusion plate).
Figure showing comparison with that of the conventional example

FIG. 5 is a perspective view of a conventional lighting device.

6 is an optical path diagram of a reflecting mirror portion of FIG.

FIG. 7: Path diagram of light restricted by critical angle of glass tube

[Explanation of symbols]

 1 Cold Cathode Fluorescent Lamp 6 Light Diffusing Plate 7 Reflector 7a 1st Curved Surface of Reflector 7b 2nd Curved Surface of Reflector

Claims (1)

[Claims] 1. A linear light source, a light diffusing plate for covering the front of the linear light source, and a reflecting mirror arranged behind the linear light source, wherein the reflecting mirror has a first curved surface and the first curved surface. And a second curved surface provided in the center of the illuminating device, wherein the linear light source is located at the focal point coordinates of the first curved surface.