JPH09306222A - Surface light source device for back light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve illumination efficiency of a planar light source device and enable power consumption to be reduced by employing a reflection process to be applied to a back face of a light guide plate as plural substantially reverse-V letter shaped reflection cut parallel to the axis of a light source and setting the maximum interval between the mutual cuts thereof to a specific value or less and the cutting depth to a specific value or less. SOLUTION: A reflection process 3 to be applied to a back face 2b of a light guide plate 2 made of crystal resin is cut in a substantial reverse-V shape and employed as a reflection cut 4a. The reflection cut 4a is parallel to an axis X of a light source 3. An interval H of the reflection cut 4a is specified as 1.2 at maximum, and a cutting depth D as 20μm. The interval H and the depth D are specified as the maximum dimension or less, and whereby the light non-uniformity generated on the radiation face 2c of the light guide plate 2 can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight used as a light source for illumination from the back when a liquid crystal display device having no self-luminous function on the display screen such as a portable or in-vehicle television receiver is adopted. The present invention relates to a surface light source device.

[0002]

2. Description of the Related Art FIG. 3 shows an example of the configuration of a conventional surface light source device 90 for a backlight, in which an axis X is aligned with an end surface 91a of a light guide plate 91 formed of a transparent material such as resin. In addition, a substantially linear light source 92 such as a cold cathode fluorescent lamp is provided, and light is introduced into the light guide plate 91.

Then, the light introduced into the light guide plate 91 is reflected by the dots 9 printed on the back surface 91b by, for example, white paint.
The liquid crystal display device 20 is illuminated from the rear surface after being reflected by the reflection processing 93 formed as 3a to emit light from the irradiation surface 91c side and diffused by the diffusion plate 94.

At this time, since the brightness varies depending on the length of the light source 92, the dots 93a are arranged so as to increase in density as the distance from the light source 92 increases. The difference in brightness that occurs is corrected so that the entire surface of the liquid crystal display device 20 is illuminated with uniform brightness.

[0005]

However, in the above-described conventional surface light source device 90 for a backlight, the dots 9 are formed by means such as a mirror surface having excellent reflection efficiency.
In the case of 3a, since the mirror surface does not diffuse the reflected light, light unevenness is generated on the irradiation surface 91c at a portion where the density is rough such as a portion near the light source 92.

To solve this problem, the dot 9
It is necessary to provide 3a with sufficient diffusivity for the reflected light. For example, the dots 93a must be formed with a white paint whose surface is a fine uneven surface, and the reflection efficiency is improved. As a result, the illumination efficiency of the backlight surface light source device 90 is reduced, and a problem arises that the light source 92 is required to have a large output and the power consumption is increased. It has become one.

[0007]

As a specific means for solving the above-mentioned conventional problems, the present invention is for a backlight in which the back surface of a light guide plate is subjected to a reflection treatment for correcting the distance from a light source. In the surface light source device, the reflection treatment is a plurality of reflection cuts formed by providing a substantially inverted V-shaped cut parallel to the axis of the light source on the back surface of the light guide plate, and the reflection cuts are formed between the cuts. It is an object of the present invention to provide a surface light source device for a backlight, which has a maximum gap of 1.2 mm or less and a cut depth of 20 μm or less.

[0008]

Next, the present invention will be described in detail based on an embodiment shown in the drawings. 1 and FIG.
What is indicated by is a backlight surface light source device according to the present invention, and this backlight surface light source device 1 is composed of a light guide plate 2, a light source 3, a reflection treatment 4 and a diffusion plate 5. Is similar to that of the conventional example.

The light guide plate 2 is made of a transparent material such as resin, and the light source 3 is a fluorescent lamp arranged along the axis X along the end face 2a of the light guide plate 2. The diffusion plate 5 is, for example, a white translucent resin plate having a diffusion function, and is an irradiation surface 2c of the light guide plate 2.
This is also similar to the conventional example in that the diffuser plate 5 diffuses the reflected light from the reflection processing 4 and illuminates the liquid crystal display device 20 from the back surface.

Here, in the present invention, the reflection treatment 4 is a reflection cut 4a formed as a substantially inverted V-shaped cut formed on the back surface 2b of the light guide plate 2, and the reflection cut 4a is formed. It is formed by making a cut having a substantially inverted V-shaped cross section in parallel with the axis X of the light source 3.

At this time, the reflection processing 4 is supposed to correct the decrease in brightness as the distance from the light source 3 increases as described above, and this correction is performed at a short distance from the light source 3. In the part, the distance H between the reflection cuts 4a
Is wider, and the reflection cut 4 increases as the distance increases.
This is performed by setting the interval H between a to be narrow and adjusting the amount of reflected light.

In addition, in the present invention, the maximum value of the interval H when making a cut in the reflection cut 4a is defined as 1.2 mm, and the depth D when making a cut at the same time.
Is defined as 20 μm, and this interval H
By defining the depth and the depth D to be equal to or less than the above dimensions, it is possible to prevent uneven light generated on the irradiation surface 2c of the light guide plate 2 and improve the illumination efficiency of the backlight surface light source device 1. It is what

Next, the operation and effect of the backlight surface light source device 1 of the present invention having the above structure will be described. As described above, the reflection treatment 4 is the reflection cut 4a configured as a substantially inverted V-shaped cut, so that the reflection cut 4a refracts the light arriving from the light source 3 in the member on which the light guide plate 2 is formed. Due to the difference between the refractive index and the refractive index of the atmosphere, the light is totally reflected and directed toward the irradiation surface 2c.

That is, the surface of the reflection cut 4a on the side facing the light source 3 acts as a mirror surface and has a high reflection efficiency, but on the other hand, the diffusivity is poor and the irradiation surface 2c is In the direction orthogonal to the axis X of the light source 3, reflected light that does not spread so much is generated, and as described in the above-mentioned conventional example, the possibility of light unevenness is high.

Therefore, in the present invention, the distance H between the reflection cuts 4a is defined to be 1.2 mm or less at the maximum even at the position closest to the light source 3 which becomes the widest, so that the light reflected from the adjacent reflection cuts 4a can be obtained. It is intended to prevent the occurrence of light unevenness as an overlap between the two.

In determining the maximum size of the interval H, the surface light source device 1 for a backlight of this type in the present situation is used.
Among the cold cathode fluorescent lamps used as the light source 3 of the above, the one having the smallest tube diameter φ, specifically, the one having the tube diameter φ of about 2 mm is used as a reference, and the light from this cold cathode fluorescent lamp is irradiated. It is set by calculating the width of the reflected light when projected on the surface 2c.

The maximum value of the depth D of the cut is determined in relation to the maximum dimension of the interval H, that is, the maximum dimension of the interval H on the back surface 2b of the portion closest to the light source 3. Is set, the value of the interval H of the part farthest from the light source 3 is set in view of the brightness correction described above, and adjacent reflection cuts 4a overlap each other at the interval H at this time. The maximum value is set by setting the values so that they do not interfere with each other.

Within the range of this maximum value, the irradiation surface 2c
With respect to the above, it is sufficient to set the depth of cut D that provides the most preferable light distribution characteristic. As a result of trial manufacture and examination by the inventor for forming the present invention, the most preferable result was obtained when the depth D of the above-mentioned incision was set to about 11 μm.

Therefore, according to the present invention, the reflection processing 4 is formed into a reflection cut 4a having a substantially inverted V shape, and the interval H between the reflection cuts 4a is set to 1.2 mm or less, and
By setting the cutting depth D to be 20 μm or less, it is possible to prevent light unevenness from occurring on the irradiation surface 2c even though the reflection efficiency of the reflection processing 4 is increased. A reference numeral 6 in the drawing is a reflecting mirror provided to more efficiently introduce the light from the light source 3 into the light guide plate 2.

[0020]

As described above, according to the present invention, the reflection treatment is a plurality of reflection cuts formed by providing the back surface of the light guide plate with substantially V-shaped cuts parallel to the axis of the light source.
The reflection cuts have a maximum distance between the cuts of 1.2 mm or less and a depth of cut of 20 μm or less, so that the surface efficiency of the light source for the backlight is improved. Nonetheless, it is possible to improve the illumination efficiency of this type of surface light source device for a back light without causing light unevenness on the irradiation surface and to achieve extremely excellent effects such as reduction of power consumption.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a surface light source device for a backlight according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view showing a conventional example.

[Explanation of symbols]

 1 ... Surface light source device for backlight 2 ... Light guide plate 2a ... End face 2b ... Rear surface 2c ... Irradiation surface 3 ... Light source 4 ... Reflection treatment 4a ... Reflection cut 5 ... Diffuser 20 ... Liquid crystal Display device D: Reflection cut depth H: Reflection cut interval X: Light source axis

Claims (1)

[Claims] 1. A surface light source device for a backlight, wherein a back surface of a light guide plate is subjected to a reflection process in which a distance from a light source is corrected, and the reflection process is performed on the back face of the light guide plate substantially parallel to an axis of the light source. A plurality of reflection cuts are formed by providing inverted V-shaped cuts, and the reflection cuts have a maximum gap between the cuts of 1.2 mm or less and a cut depth of 20 μm or less. A surface light source device for a backlight, comprising: