JP2868085B2 - Planar light source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar light source used for a display backlight, an illuminated operation switch and the like, and more particularly to a planar 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.

[0003] (hereinafter referred to as LED.) Light-emitting diodes have also been partially utilized as a backlight wells light source. 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.
In the present circumstances are selectively used as L, backlight wells of white light emission using an LED is largely unknown.

As a white light source or a monochromatic light source, there has been an attempt to convert the color by surrounding a blue LED chip with a resin containing a fluorescent substance in some cases. To be exposed to the light,
Deterioration of the fluorescent substance becomes a problem, particularly in organic fluorescent pigments. Further, the ionic organic dye causes electrophoresis in the vicinity of the chip due to a DC electric field, and the color tone may change. Further, a conventional blue LED does not have a sufficient output for color conversion with a fluorescent substance, and even if color conversion is performed, it is not practical.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and an object of the present invention is to provide a white light-emitting surface which can be mainly used as a backlight by using LEDs. To provide a planar light source capable of observing uniform white light emission while realizing a light source, and to provide a planar light source capable of emitting light of any color other than white, and to provide highly reliable LED characteristics. And to use it for various operation switches.

[0006]

According to a planar light source of the present invention, a blue LED is optically connected to at least one portion of an end face of a transparent light guide plate, and further, any one of the main surfaces of the light guide plate is provided. A fluorescent scattering layer (hereinafter, referred to as a fluorescent scattering layer) applied in a state where a fluorescent substance that emits fluorescence when excited by light emission of the blue light emitting diode and a white powder that scatters light are mixed.
The main surface on the side of the fluorescent scattering layer is called a second main surface. ), A part of the light emitted from the blue light emitting diode is wavelength-converted by the fluorescent scattering layer, and the main surface of the light guide plate opposite to the fluorescent scattering layer (hereinafter the main surface on the light emission observation side is the first main surface). The surface is observed from the side.)

FIG. 1 is a plan view of a light guide plate 2 of a planar light source according to the present invention as viewed from a fluorescent scattering layer 3 side. The light guide plate 2, for example acrylic, made of a transparent material such as glass, by blue LED1 is embedded in the end face of the light guide plate 2, 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. As shown in (1), it is possible to embed the blue LED 1 as well as to bond the blue LED or to guide the light emission of the blue LED to the end face of the light guide plate 2 using an optical fiber or the like.

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 the LEDs may be connected to all four end faces if the light guide plate is rectangular, 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.

[0009]

FIG. 2 is a schematic sectional view showing a case where the planar 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.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 A fluorescent scattering layer 3 was formed by screen printing on one surface of an acrylic plate having a thickness of about 2 mm in a dot pattern shown in FIG. The fluorescent scattering layer 3 is composed of a red fluorescent pigment FA-001 manufactured by Shinloygi Chemical and a green fluorescent pigment manufactured by F-
A-005 was mixed with an equal amount of a fluorescent pigment, and barium titanate as a white powder was mixed at a weight ratio of 1: 5, and the mixture was dispersed in an acrylic binder and printed. .

Next, the acrylic plate on which the fluorescence 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.

The light guide plate 2 is provided with two holes at its end face,
The emission wavelength is 480 nm in the hole. A blue LED made of a gallium nitride-based compound semiconductor having an emission output of 1200 μW
Are embedded one by one to obtain a planar light source of the present invention. When the blue LEDs of the planar light source were simultaneously turned on, a slightly yellowish white substantially uniform planar 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 Lu from BASF.
mogenF Yellow-083 and Orange-240 as an orange fluorescent dye were mixed in almost equal amounts,
The same procedure as in Example 1 was carried out except that a mixture of a fluorescent dye dissolved in butyl carbitol acetate and barium titanate as a white substance at a weight ratio of 1 (dye): 200 was used. When the planar light source of the present invention was obtained, 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.

[0015]

As described above, the planar light source of the present invention uses a blue LED, and has a fluorescent substance and a white powder on one surface of the light guide plate which contains a fluorescent substance capable of wavelength conversion by the blue LED. , It is possible to realize a planar light source using LEDs with excellent reliability. In addition, since the white powder of the fluorescent scattering layer has an effect of reflecting and diffusing the light whose wavelength has been converted by the fluorescent substance, the amount of the fluorescent substance used can be reduced. More advantageously, there is no direct contact between the LED chip and the phosphor, so that the phosphor is less deteriorated and can be used for a long time.
It does not cause a color change in the surface light source Te. 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, as the side for exciting the fluorescent scattering layer, the emission output of the blue LED to be used is most preferably 200 μW.
With the above structure, it is possible to realize a large area bright light source by efficiently converting the wavelength by the fluorescent substance. Thus, the planar light source of the present application
Not only wells light source or the like, may also be utilized to illuminated operation switch or the like which utilizes 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 one embodiment of the present invention as viewed from a fluorescent scattering layer side .

Schematic sectional view when mounted as backlight wells planar light source of an embodiment of the present invention; FIG.

[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 (2)

(57) [Claims] 1. A blue light-emitting diode is optically connected to at least one portion of an end surface of a transparent light guide plate, and is excited by light emission of the blue light-emitting diode on one of main surfaces of the light guide plate. A fluorescent substance which emits fluorescent light and a white powder which scatters the fluorescent light, and has a fluorescent scattering layer applied in a mixed state. The light emission of the blue light emitting diode is wavelength-converted by the fluorescent scattering layer, and the fluorescence scattering is performed. A planar light source which is observed from the main surface side of the light guide plate opposite to the layer. 2. The planar light source according to claim 1, wherein the blue light emitting diode has a main emission wavelength shorter than 500 nm and an emission output of 500 μW or more.