JPH1097200A - Light source - Google Patents

Abstract

(57) [Problem] To realize a light source capable of emitting white light which can be mainly used as a backlight by using an LED. Uniform white light emission can be observed. It can emit light of any color other than white, and is used for various operation switches, etc., utilizing the characteristics of LEDs with excellent reliability. SOLUTION: The light source has a fluorescence scattering layer optically connected to a gallium nitride compound semiconductor emitting blue light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source used mainly for a backlight of a display, an illuminated operation switch and the like, and more particularly to a light source which can be suitably used as a backlight of a liquid crystal display.

[0002]

2. Description of the Related Art As a planar light source for a backlight of a liquid crystal display generally used for a notebook personal computer, a word processor, etc., for example, an EL or a cold cathode tube is used. EL
Is itself a planar light source, the cold cathode fluorescent lamp is a planar light source using a diffusion plate, and most of the backlights emit white light at present.

On the other hand, light emitting diodes (hereinafter, referred to as LEDs) are also partially used as light sources for backlights. However, when white light emission is obtained using an LED, the emission output of a blue LED is only about several tens of μW conventionally,
In order to realize white light emission using other red LED and green LED, there is a disadvantage that the characteristics of each color light emitting LED are hardly matched and a color change is large. Also, the three primary colors L
Even if the EDs are assembled and arranged at the same geometric position on the same plane, it is impossible to provide a uniform white light source because the LEDs are visible at a close position as a backlight. Was. Therefore, the surface light source of a currently white liquid crystal backlight is a cold cathode tube for a large size, and an E for a small to medium size.
At present, backlights that emit white light using LEDs are hardly known.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve such a drawback, and an object of the present invention is to provide a light source capable of emitting white light which can be mainly used as a backlight by using an LED. In addition to providing a light source capable of observing uniform white light emission, and also providing a light source capable of emitting light of any color other than white, utilizing the characteristics of an LED with excellent reliability, An object of the present invention is to provide a light source that can be used for a switch or the like.

[0005]

The light source of the present invention has a fluorescent scattering layer optically connected to a gallium nitride compound semiconductor emitting blue light. The fluorescence scattering layer has a fluorescent substance that emits fluorescence when excited by blue light emission of the gallium nitride-based compound semiconductor, and a powder that scatters the fluorescence. The blue light emission of the gallium nitride-based compound semiconductor is wavelength-converted by the fluorescent substance contained in the fluorescent scattering layer, further scattered by the powder, and emitted to the outside.

FIG. 1 is a plan view of a light guide plate 2 of a light source according to an embodiment of the present invention as viewed from the side of a fluorescent scattering layer 3. The light guide plate 2 is made of, for example, a transparent material such as acrylic or glass, and the blue LED 1 is embedded in an end surface of the light guide plate 2 so that the light guide plate 2 and the blue LED 1 are optically connected. In the present invention, that the blue LED 1 and the end face of the light guide plate 2 are optically connected means that light of the blue LED is introduced from the end face of the light guide plate 2 in a simple manner. The blue LED 1 is buried, as shown in FIG. 2, and the blue LED is adhered to the end face of the light guide plate 2 using an optical fiber or the like.
This can be realized by guiding D emission.

Next, the fluorescent scattering layer 3 is coated with an ink prepared by mixing a fluorescent substance and a white pigment so that a desired color can be observed. The fluorescent light is scattered in the light guide plate 2 by a white pigment. In particular, in FIG. 1, the fluorescence scattering layer 3 is formed in a dot shape, and the fluorescence scattering per unit area on the second main surface side as approaching the blue LED 1 so that the surface luminance on the first main surface side becomes constant. The pattern is such that the area of the layer 3 is reduced, and the area of the end of the second main surface farthest from the blue LED 1 is slightly smaller than the maximum area. Here, ■ in FIG. 1 represents the pattern of the fluorescent scattering layer 3. Although FIG. 1 shows a structure in which two blue LEDs are arranged on one end face, it is needless to say that LEDs may be connected to all four end faces if the light guide plate is square, and the number of LEDs is also limited. It does not do. further,
Depending on the arrangement of the LEDs, the coating shape and the coating state of the fluorescent scattering layer can be appropriately changed so that the emission observed from the first main surface side is made uniform in a planar manner.

[0008]

FIG. 2 is a schematic sectional view showing a case where the light source of the present invention is mounted as, for example, a backlight of a liquid crystal panel. In this, a scattering reflection layer 6 made of, for example, barium titanate, titanium oxide, aluminum oxide, and the like, and a base 7 made of, for example, Al are laminated on the second main surface side of the planar light source shown in FIG. A reflection plate is provided, and a light diffusion plate 5 having an uneven surface is provided on the first main surface side. These configurations are not particularly different from a backlight using a cold cathode tube as a light source.

First, as shown by the arrow in FIG.
Light emitted from 1 is partially radiated outside the light guide plate near the chip, but most of the light reaches the end face of the light guide plate while repeating total reflection in the light guide plate 2. The light that reaches the end face is reflected by the reflection film 4 formed on the entire end face, and repeats total reflection. At this time, a part of the light is scattered by the fluorescent scattering layer 3 provided on the second main surface side of the light guide plate 2, and a part of the light is absorbed by the fluorescent substance, and the wavelength is simultaneously converted and emitted. The emission color observed from the first main surface side of the light plate 2 can be obtained by combining these lights. For example, in the planar light source provided with the fluorescent scattering layer 3 made of an orange fluorescent pigment and a white pigment, the emission color of the blue LED can be observed as white due to the above-described operation. Further, the color tone can be arbitrarily adjusted by the kind of the fluorescent substance and the mixing ratio of the white pigment. In particular, in the present invention, the emission wavelength of one blue LED has a main emission peak shorter than 500 nm, and the emission output thereof is 200 μW
As described above, more preferably, an output of 300 μW or more is required. If the emission wavelength is 500 nm or more, it is difficult to realize all colors, and the emission output is 200 μW
If the number is smaller than that, even if the number of blue LEDs optically connected to the end face of the light guide plate is increased, it tends to be difficult to obtain a light source of planar light emission with sufficient brightness and uniformity.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 One side of an acrylic plate having a thickness of about 2 mm
The fluorescent scattering layer 3 was formed by screen printing in the dot pattern shown in FIG. The fluorescent scattering layer 3 was prepared by mixing a fluorescent pigment obtained by mixing equal amounts of FA-001 manufactured by Shinroihi Chemical Co., a red fluorescent pigment and FA-005 manufactured by the company, a green fluorescent pigment, and barium titanate as a white powder in a weight ratio. 1:
The mixture was mixed at a ratio of 5 and dispersed in an acrylic binder to form a print.

Next, the acrylic plate on which the fluorescent scattering layer is formed as described above is cut in accordance with a desired pattern, and all the end faces (cut surfaces) of the acrylic plate are polished. By forming No. 4, the light guide plate 2 on which the fluorescent scattering layer 3 was formed was obtained.

Holes are provided at two places on the end surface of the light guide plate 2, and the light emission wavelength is 480 nm and the light emission output is 1200 μm.
Blue L made of gallium nitride based compound semiconductor having W
By embedding EDs one by one, a light source according to an embodiment of the present invention was obtained. When the blue LEDs of this light source were simultaneously turned on, a slightly yellowish white almost uniform surface light emission was obtained from the light emission observation surface side of the light guide plate 2. Further, a light diffusion plate 5 pre-matted on the emission observation surface side and a reflection plate coated with a barium titanate layer 6 on an Al base 7 on the fluorescence scattering layer 3 side are installed on the side of the fluorescence scattering layer 3 to provide a backlight. When the light source was used, white light emission with a completely uniform surface was obtained from the light diffusion plate 5 side. The brightness was 55 cd / m ² .

[Example 2] The fluorescent scattering layer 3 was used as a yellow fluorescent dye by Lumogen F Yellow of BASF.
-083 and Orange-2 manufactured by the company as an orange fluorescent dye
And a mixture of a fluorescent dye obtained by dissolving them in butyl carbitol acetate and barium titanate as a white substance at a weight ratio of 1 (dye): 200. Other than that, when the light source of the present invention was obtained in the same manner as in Example 1, substantially uniform planar light emission was observed. Furthermore, when the light source for a backlight was used in the same manner, completely uniform planar light emission was observed.

[0014]

As described above, the light source of the present invention has the following features.
Using a blue-emitting gallium nitride-based compound semiconductor and having a fluorescent scattering layer containing a fluorescent substance capable of wavelength conversion by a blue LED on one side of the light guide plate and a powder that scatters fluorescent light, It has become possible to realize a light source using an LED having excellent characteristics. Moreover, the powder of the fluorescent scattering layer reflects the light whose wavelength has been converted by the fluorescent substance,
Due to the effect of diffusion, the amount of fluorescent substance used can be reduced. More advantageously, since the LED chip and the fluorescent substance do not come into direct contact with each other, the deterioration of the fluorescent substance is small, and the color tone of the light source does not change over a long period of time. Further, with respect to the color tone, any color tone including white can be provided by changing the kind of the fluorescent substance and the white powder, the mixing amount, and the like.

On the other hand, on the side for exciting the fluorescent scattering layer, the emission output of the blue LED most preferably used is 200 μW.
With the above structure, it is possible to realize a bright light source having a large area by efficiently converting the wavelength by the fluorescent substance. As described above, the light source of the present application can be used not only for a light source for a backlight or the like but also for an illuminated operation switch or the like using a fluorescent substance.

[Brief description of the drawings]

FIG. 1 is a plan view of a light guide plate of a planar light source according to an embodiment of the present invention as viewed from a fluorescent scattering layer side.

FIG. 2 is a schematic cross-sectional view when a planar light source according to one embodiment of the present invention is mounted as a backlight.

[Explanation of symbols]

 1 ... Blue LED 2 ... Light guide plate 3 ... Fluorescence scattering layer 4 ... Reflection layer 5 ... Light diffusion plate 6 ... Diffusion reflection Layer 7 ... Al base

Claims (3)

[Claims] 1. A light source having a fluorescence scattering layer optically connected to a gallium nitride compound semiconductor emitting blue light, wherein the fluorescence scattering layer is excited by emission of the gallium nitride compound semiconductor to emit fluorescence. A light source comprising: a fluorescent substance that emits light; and a powder that scatters fluorescence. 2. The light source according to claim 1, wherein the powder is white powder and the light source emits white light. 3. A fluorescent scattering layer having a fluorescent substance which emits fluorescence when excited by light emission of a blue light emitting diode, a white powder which scatters fluorescent light of the fluorescent substance, and blue light emission which irradiates the fluorescent scattering layer with light. A light source comprising a diode, wherein the wavelength of the light emitted from the blue light emitting diode is converted by the fluorescent substance contained in the fluorescent scattering layer, scattered by the white powder, and observed outside.