JPH04369620A - Illuminator - Google Patents

Abstract

PURPOSE:To obtain an illuminator having high quality which is much brighter than a conventional illuminator and has a uniform light emission distribution by arranging a light source at the entire periphery of the outer peripheral end surface a transparent plate. CONSTITUTION:The illuminator is constituted by arranging the transparent plate 1 provided with a diffusion system layer 5 formed of milk-white dots linear patterns on at least one surface and light sources 6 arranged adjacently to the end surface of the transparent plate 1; and the light sources 6 are arranged adjacently to all the other peripheral end surfaces of the transparent plate 1. The transparent plate 1 is nearly rectangular, polygonal, or circular. Consequently, high brightness and good brightness uniformity are obtained while the thickness is kept as usual as it is, and the temperature distribution on the light emission surface is flat. The quality characteristics such as the brightness irregularity and color irregularity of a liquid crystal display unit combined with it can be improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin lighting device.

More specifically, the present invention relates to an illumination device that includes a rod-shaped light source and a light guide system and is used as a backlight for a liquid crystal display or the like.

0003

2. Description of the Related Art Conventionally, in a lighting device comprising a light source and a light guide system, a light source 6 is arranged adjacent to one or two end surfaces 4 of a generally rectangular transparent plate 1, as shown in FIG.

0004

However, such conventional illumination devices have low brightness and are insufficient as backlights for liquid crystal displays, particularly for liquid crystal displays capable of color display. Furthermore, when the amount of light from the light source is increased in order to increase the brightness, the amount of heat generated by the light source also increases, resulting in a problem in that the temperature in the vicinity of the light source locally increases extremely. In the first place, backlights set on the back side of liquid crystal displays require uniform, even, high-intensity illumination, but from another perspective, uniformity in temperature distribution is also required. The reason for this is that optical characteristics such as transmittance of a liquid crystal display are a function of temperature, and the characteristics change significantly depending on the ambient temperature. Therefore, if the surface temperature of the backlight varies from place to place, serious quality problems such as uneven brightness and color of the display will occur, so uniformity of temperature distribution as well as brightness uniformity has been a technical issue.

Therefore, in order to solve these conventional problems, the present invention provides an illumination device that is thin as before, has high brightness, good brightness uniformity, and has a flat temperature distribution on the light emitting screen. The purpose is to

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the lighting device of the present invention has the following features: (1) A diffusion layer formed of opalescent dots or linear patterns is provided on at least one surface. (2) The transparent plate has a generally rectangular, polygonal, or circular shape. (3
) The transparent plate is characterized in that the largest area portion of the diffused reflection layer is arranged approximately at the center of the transparent plate.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. In FIG. 1, a transparent plate 1 is a generally rectangular transparent plate having a constant thickness, and at least a light-emitting surface 2 and a light-emitting surface 3, preferably all surfaces, are mirror surfaces (smooth surfaces). The material of the transparent plate 1 may be any transparent material as long as it has low light absorption and a refractive index higher than that of air, but a refractive index of 1.41 or more is particularly desirable, and acrylic resin, polycarbonate resin, polystyrene resin, glass, etc. are used. . When the refractive index is 1.41 or more, the critical angle is 45 degrees or less, and all the light rays incident on the transparent plate 1 can be totally reflected by the mirror surface that is approximately perpendicular to the end surface 4.

A diffusion system 5 is provided on the opposite light-emitting surface 3 of the transparent plate 1 by printing or adding a shape. The diffusion system 5 is formed in the shape of a dot or a thin line on the anti-light-emitting surface 3 and has a certain distribution with respect to the mirror surface. This is because the light rays incident from the end surface 4 of the transparent plate 1 are totally reflected by the mirror surfaces that are approximately perpendicular to the end surfaces 4 of the light-emitting surface 2 and the anti-light-emitting surface 3, and travel further through the transparent plate 1 from the end surface 4. On the other hand, this is because the light reaches the diffusion system 5 with a certain probability and is necessary for a part of the light to exit from the light exit surface 2.

The reason why it is desirable that all the surfaces constituting the transparent plate 1 be mirror surfaces is that since the transparent plate 1 is plate-shaped, the area of the other surfaces is small compared to the light-emitting surface 2 and the anti-light-emitting surface 3. Although the amount of light is small, the probability that the light rays remain in the transparent plate 1 increases due to the effect of total reflection, and as a result, the light output efficiency increases. For example, when an approximately rectangular acrylic plate is used as the transparent plate 1, the critical angle is about 42 degrees, so unless the light rays incident from the end face 4 reach the diffusion system 5, they will not be transmitted from the end face other than the end face opposite to the end face 4. Idemitsu will not be emitted.

A light source 6 is arranged adjacent to the end surface 4 of the transparent plate 1. As the light source 6, a fluorescent tube is used. Any light source may be used, such as an incandescent lamp, a linearly arranged light emitting diode, or light introduced through an optical fiber, but a fluorescent tube is suitable depending on conditions such as luminous efficiency, color, and handling. The light source 6 is arranged all around the end surface 4 of the transparent plate 1, and the light rays from the light source 6 are
It is guided to the transparent plate 1. By disposing the light source 6 all around the end surface 4 of the transparent plate 1, compared to the conventional one or two light sources,
It is possible to obtain 2 to 4 times more brightness.

A diffusion film 7 is arranged adjacent to the light output surface 2 side of the transparent plate 1, and a diffused reflection plate 8 is arranged adjacent to the opposite light output surface 3 side. The diffuser film 7 and the diffused reflection plate 8 are arranged adjacent to the transparent plate 1 with a slight air layer interposed therebetween, and this air layer is necessary for total reflection at the critical angle described above. The diffusion film 7 diffuses and uniformizes the light rays emitted from the light emitting surface 2. The diffused reflection plate 8 further returns to the diffusion film 7 side the light rays that have been diffused by the diffusion system 5, reflected by the light output surface 2, and passed through the anti-light output surface 3, and the light rays that have been reflected by the diffusion film 7 and passed through the transparent plate 1. do the work. Also, a reflective sheet 9 is provided to cover the light source 6.
is placed. The reflective sheet 9 serves to guide the light rays from the light source 6 to the end surface 4, and is made of a white plastic sheet or a molded product coated with silver, aluminum, or the like.

[0012] The transparent plate 1 can be polygonal or circular, and by doing so, the outer peripheral end face can be made long. For a hexagon as shown in Figure 2, it is approximately 6% of the corresponding rectangle, and for a circle as shown in Figure 3, it is approximately 1%.
By arranging the light source 6 all around the outer peripheral end face, the brightness of the entire lighting device can be further increased as a result.

In the distribution of the diffusion system 5, the area ratio is small in a portion close to the light source, and large in a portion away from the light source. Figure 1
, in a point-symmetrical shape as shown in Figures 2 and 3, on a line passing through the center in all directions, the absolute value and distribution of the area ratio may change depending on the direction, but as shown in Figure 4. It has a pattern, and its area ratio has a distribution as shown in schematic diagram 5. That is, the central portion has the largest area ratio among all patterns. The relationship between the position on the transparent plate 1 and the area ratio of the diffusion system 5 is determined by using the recent development of computer simulation technology instead of the conventional trial and error or approximate formula method. Here, the pattern shown in FIG. 4 is an example, and the shape of the points may be round or other irregular shapes.
Also, it may be a line instead of a point.

The directions of the light rays incident on the transparent plate 1 from the end face 4 are multidirectional compared to the conventional case of two light sources, and the maximum area ratio of the diffusion system 5 is at the center. Therefore, since the range of the incident light from the end face 4 is narrow, the brightness distribution tends to be uniform. FIG. 7 is a graph showing the temperature distribution on the screen at room temperature when the lighting device of the present invention shown in FIG. 1 is turned on. It can be seen that the temperature above the light source 6 is high, and the temperature does not rise much at the center of the screen. FIG. 8 is a graph showing the temperature distribution on the screen when the conventional lighting device shown in FIG. 6 is turned on. In order to make the brightness on the screen obtained in this case equivalent to that in FIG. 1, approximately twice as much current is passed through the light source 6. Therefore, it was found that the temperature above the light source 6 rose extremely, and the temperature rose by 30 to 40 degrees Celsius compared to the room temperature of 25 degrees Celsius. As a result of actually mounting MIM-type active color liquid crystal panels or STN-type passive color liquid crystal panels and evaluating color unevenness and brightness unevenness, we found that conventional technology cannot be put to practical use unless special heat dissipation means are added. I understand. In the example according to the present invention, a beautiful color image with very little color unevenness was easily obtained over the entire screen.

[0015]

[Effects of the Invention] According to the present invention, as explained above,
By arranging the light sources all around the outer peripheral end surface of the transparent plate, it is possible to provide a high-quality lighting device that is much brighter than conventional lighting devices and has a uniform light emission distribution. Moreover, by making the outer shape of the transparent plate polygonal or circular, an even brighter lighting device can be provided. Furthermore, since the temperature distribution on the light emitting screen can be made flat, it has the great effect of improving the quality characteristics such as brightness unevenness and color unevenness of the liquid crystal display combined with this.

[Brief explanation of drawings]

FIG. 1 (a) A plan view showing one embodiment of the present invention. (b) A sectional view showing one embodiment of the present invention.

FIG. 2 is a plan view showing another embodiment of the present invention.

FIG. 3 is a plan view showing another embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an embodiment of the diffusion system of the present invention.

FIG. 5 is an explanatory diagram showing the area ratio of the diffusion system of the present invention.

FIG. 6 is a plan view showing a conventional technique.

FIG. 7 is a graph showing the temperature distribution on the screen when the lighting device of the present invention is turned on.

FIG. 8 is a graph showing the temperature distribution on the screen when the conventional lighting device is turned on.

[Explanation of symbols]

1 Transparent plate 4 End face 5. Diffusion system 6. Light source

Claims (3)

[Claims] 1. A lighting device comprising: a transparent plate provided with a diffusion layer formed of opalescent dots or linear patterns on at least one surface; and a light source disposed adjacent to an end surface of the transparent plate. A lighting device characterized in that a light source is arranged adjacent to all outer peripheral end surfaces of a transparent plate. 2. The lighting device according to claim 1, wherein the transparent plate is approximately rectangular, polygonal, or circular. 3. The lighting device according to claim 1, wherein the largest area portion of the diffuse reflection layer of the transparent plate is disposed approximately at the center of the transparent plate.