JPH1139917A - High color rendering property light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a color rendering property, to reduce costs and to enhance efficiency by providing a wavelength conversion member containing organic coloring matter receiving light from at least one light emitting element and generating output light so as to produce combination light in the case of improving color effects through additive color mixing of the light from the plural light emitting elements. SOLUTION: A color rendering property is enhanced by applying a wavelength conversion material to a white light source whose light emitting elements are light emitting diode LED chips so as to convert wavelengths. Concretely, the LED chips 3, 4, 5 are coated by coloring matter rhodamine 19 dissolving- dispersed epoxy resin 6 so as to obtain an LED light source 10. Since a phosphor, including rhodamine 19, is powder, the same is mixed with epoxy resin for fixing the whole LED so as to form the wavelength conversion material. The wavelength conversion material is place in a reflection cup 2 containing the LED chips so as to reflect forward the light generated from the LED chips 3, 4, 5, and the light converted by the phosphor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source, and more particularly to a light source having improved color rendering by utilizing wavelength conversion.

[0002]

BACKGROUND OF THE INVENTION In recent years, many illumination light sources have been used, and their characteristics have been continuously improved. In addition to the color temperature, luminous flux, efficiency, and the like, the characteristics of the illumination light source include color rendering as one of the important characteristics. In order to substitute natural light, a material having good color rendering properties for natural light is desired. As a method of quantitatively evaluating color rendering properties, CIE 196
There is an evaluation method set in 5 years and partially revised in 1974 (hereinafter referred to as "CIE second edition evaluation method"). In Japan, the evaluation method of CIE 2nd edition is adopted in JIS Z8726. It is common to evaluate the color rendering properties based on the average color rendering index (Ra) defined by these evaluation methods, and the description will be made using Ra in this specification.

[0003] The closer the average color rendering index Ra is to 100, the better the color rendering properties. The color rendering index of the incandescent lamp is 100. The requirements for the color rendering properties of the light source differ depending on where the light source is used.
Ra is required to be 60 or more. Further, a light source having a high color rendering property is preferable because a larger brightness feeling can be obtained than a lamp having a low color rendering property even at the same illuminance.

Conventionally, in order to improve the color rendering of a light source,
A lot of work has been done. For example, in a fluorescent lamp, the energy of a strong line spectrum of 253.7 nm generated by low-pressure mercury discharge is received by a fluorescent film and converted into visible light to perform color correction to improve color rendering. Therefore, the color rendering properties can be improved by appropriately selecting the phosphor used for the fluorescent film and the structure of the fluorescent film. In the technique disclosed in Japanese Patent Application Laid-Open No. 5-86364 (Hatakeyama et al.), The color rendering index is increased to 80 or more by using a plurality of phosphors while keeping the total luminous flux high.

[0005] Fluorescent high-pressure mercury lamps (for example, JP-A-4-24-2)
No. 34482 (Iwama)) and metal halide lamps (for example, JP-A-6-76798 (Todoroki et al.))
With the development of phosphors, color rendering properties have been improved by absorption and emission of the phosphors.

[0006] Japanese Patent Application Laid-Open No. 6-243841 discloses a technique for obtaining a mixed color illumination having high color rendering properties by housing a high-pressure sodium lamp and a high-pressure mercury lamp together in an outer tube coated with a phosphor. Each of the above examples has a configuration in which an inorganic phosphor containing a rare earth element is applied to the tube surface.

[0007] If a semiconductor light emitting diode (hereinafter, referred to as an LED) is used as an illumination light source, the life of the illumination light source may be significantly improved. Further, a curved light source or a three-dimensional light source can be configured using a large number of LEDs. For this reason, an attempt has been made to produce a full-color LED display or an LED lighting device using both a high-brightness blue and green LED developed and marketed in recent years and a conventional high-brightness red LED. In particular, white light sources made of red, green, and blue LEDs have attracted attention as near-future illumination light sources that replace conventional incandescent bulbs, fluorescent lamps, and HID lamps. In a white LED light source, it is necessary to enhance color rendering.

[0008]

As described above, in order to improve the color rendering properties of these light sources by using wavelength conversion while various types of light sources are used, a phosphor or a wavelength conversion member having properties suitable for the light source is used. Is determined. It is desired that such a wavelength conversion material be applied to a light source of the prior art to reduce manufacturing costs and obtain other benefits. Especially LED
If used as a light source, a longer-life illumination light source can be expected. Accordingly, it is an object of the present invention to provide a light source which is inexpensive, efficient and has excellent color rendering properties by a configuration not conventionally used. Still another object of the present invention is to improve the color rendering of illumination light of a semiconductor light emitting device such as an LED.

[0009]

In order to achieve the above object, a light source according to the present invention is a light source that generates illumination light by additively mixing light from a plurality of light emitting elements that generate different lights. A wavelength conversion member containing an organic dye that receives light from at least one of the light-emitting elements to generate output light, and color rendering properties of combined illumination light generated by additively mixing the output light and the illumination light. Are designed to improve the color rendering of the illumination light.

The wavelength conversion member can be made of an epoxy resin in which an organic dye is dissolved, and transparent and efficient wavelength conversion can be performed. Some dyes such as rhodamine can be used as the organic dye.

Although the present invention is effectively implemented when a light emitting diode chip is used as a light emitting element and a white light source is obtained by combining them, it is apparent that the present invention can be applied to other light emitting elements.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a white light source having a light emitting element as a light emitting diode chip (hereinafter, referred to as an LED chip) will be described below. FIG. 1A is a schematic plan view of a white LED light source 1 according to the prior art, and FIG.
It is -A side sectional drawing. For easy understanding, a sealing material such as a transparent epoxy resin covering the internal wiring, the lead wire, and the LED chip is omitted. In both figures, a blue LED chip 3 that emits blue light and a green LE that emits green light are placed on a reflective cup 2.
A D chip 4 and a red LED chip 5 that emits red light are mounted. These LED chips 3, 4, 5 are lit and emit light by conventional means well known to those skilled in the art. The light generated by the LED chips 3, 4, and 5 is radiated upward in FIG. 1B and is subjected to additive color mixing to become illumination light approximating the reference light.

The average color rendering index of the illuminating light was measured to be at most 40 by adjusting the current flowing through each LED chip of the white LED light source 1 to approximate the color temperature of the incandescent lamp. Average color rendering index 60 required for light source for general lighting
This is a considerably lower value than. Then, when the relative spectral distribution of the illumination light was measured, the measurement results shown in the graph of FIG. 2 were obtained. As is clear from the graph of FIG. 2, the relative spectral distribution of the illumination light has a relatively narrow spectrum from each LED chip, and has a large deep valley between green and red.
Then, it was presumed that the valley composed of the spectrum in the yellow region was the cause of lowering the color rendering properties.

Therefore, the inventors thought that if the valley could be filled, it would be possible to increase the average color rendering index. For this reason, L that emits orange or yellow light
Although a method of adding an ED chip has been considered, there is a disadvantage that adjustment of each color LED for making a white light source becomes complicated in addition to a problem of a location and a cost for adding an LED chip of a new color. I understand.

Therefore, the valley is filled by wavelength conversion using a wavelength conversion material to improve color rendering. It was also considered that the use of a phosphor having high efficiency and appropriate absorption and emission wavelengths would be advantageous because there would be little change in the measured light amount (generally, a decrease in efficiency and a decrease in total luminous flux). According to Stokes' law, the light from a green or blue LED chip must be converted because "the wavelength of the fluorescing radiation is always longer than the wavelength of the emitted radiation." Since the light from the LED chips 3, 4, and 5 is substantially only light in the visible light range, it is particularly desirable to efficiently convert the wavelength (there is a component that does not need to be included in illumination light such as ultraviolet light). In this case, since the ultraviolet light is converted into visible light, the change in the light intensity can be relatively suppressed.

Investigations and experiments on the materials used for wavelength conversion revealed that, in addition to the inorganic phosphor, for example, organic dyes also include suitable materials such as rhodamine-based dyes. In one embodiment of the present invention, the dye rhodamine 19
(Lambda Physiks, Federal Republic of Germany): Benzoic acid, 2-
[6- (ethylamino) -3- (ethylimino) -2,7-dimethyl-3
H-Xanthen-9-], perchlorate was selected. The absorption spectrum of rhodamine 19 dispersed in the epoxy resin was as shown in FIG. 3, and the emission spectrum was as shown in FIG. Thus, it was expected that rhodamine 19 would absorb the green peak of FIG. 2 and be suitable for filling the yellow valley.

As shown in the cross section of FIG. 5 corresponding to FIG. 1B, an LED light source 10 was obtained in which the LED chip was covered with the epoxy resin 6 in which the dye rhodamine 19 was dissolved and dispersed. The LED light source 10 is the same as the LED light source 1 shown in FIGS. 1A and 1B except for the coating with the epoxy resin 6. However, the LED light source 10 may or may not be coated with a transparent resin or the like in addition to the epoxy resin 6. Usually, since the phosphor such as rhodamine 19 is a powder, it is mixed with an epoxy resin when the entire LED is fixed with a resin, thereby constituting a wavelength conversion member. The wavelength conversion member is placed in the reflection cup 2 that houses the LED chip so that the light generated from the LED chip and the light converted by the phosphor are reflected forward. The wavelength conversion member is 3
It is not necessary to cover one LED chip, and it can be filled so as to cover only the LED chip that excites (absorbs) the phosphor.

FIG. 6 shows the relative spectral distribution of the emitted light of the white LED according to the present invention whose cross section is shown in FIG. The average color rendering index when Rhodamine 19 was used as the phosphor was about 76, which was greatly improved as compared with the average color rendering index 40 of the conventional white LED. The conventional white LED shown in FIG.
The efficiency (lm / W) of the present invention was reduced by about 10% or less as compared with the efficiency of the above, and it was found that the color rendering properties could be greatly improved without sacrificing the efficiency so much.

The phosphor for obtaining the same effect as in the present invention is not limited to the following phosphor, but in addition to the rhodamine 19 shown in the examples, the following organic,
Inorganic phosphors can also be used practically. (Organic dyes): All manufactured by Lambda Physiks Rhodamine 110: o- (6-amino-3-imino-3H-xanthen-9-yl) -benzoic acid, center of absorption wavelength is 510 nm,
Emission center wavelength is 570 nm (when dispersed in epoxy resin). DCM: 4-dicyanmethylene-2-methyl-6- (p-dimethylaminostyryl) -4H-pyran, absorption center wavelength is 472.
nm, emission center wavelength is 650 nm (when dispersed in epoxy resin) ・ DCM special (manufactured by Lambda Physiks) (inorganic phosphor) ・ Ce: There is a change in characteristics due to the composition of YAG and YAG.
The absorption center wavelength is 450 nm and the emission center wavelength is 580 nm. Organic dye materials are easy to dissolve and disperse in resins such as epoxy resin, and the dispersed particles are small and high transparency can be obtained.
This is advantageous because unnecessary scattering of transmitted light can be reduced. In addition, the range of selection of absorption and emission wavelengths is wide,
Large design freedom.

The manufacture of the LED light source embodying the present invention is as follows. First, the LED chips 3, 4,.
After arranging and wiring 5, an appropriate amount of epoxy resin 6 in which rhodamine 19, which is a wavelength conversion member, is dispersed is introduced into a reflection cup to cover the LED chip. First, at this point
The temperature is raised to 00-150 ° C. and the wavelength conversion material is cured in about 2 hours. Thereafter, the entire LED light source is cured with a transparent resin similar to the conventional one. The obtained white LED light source is energized, and the average color rendering index is measured and evaluated. In order to make the optical characteristics (including color rendering properties) of the wavelength conversion member desired, conventional means are used so that the geometric shape of the wavelength conversion member is also constant. Although the optimum value of the concentration of the phosphor with respect to the epoxy resin varies depending on the phosphor used, the concentration can be experimentally specified so as to minimize the desired color temperature, color rendering, and efficiency.

First, an LED light source that satisfies a predetermined light emitting pattern and heat radiation condition is designed by the selected LED chip. After sealing with an epoxy resin in which an organic dye is dispersed, each L
By adjusting the operating current of the ED chip, the combined illumination light is adjusted to a predetermined x.
Take y-chromaticity coordinates. The color rendering index and total luminous flux are measured. By repeating the above measurement while changing the concentration of the organic dye, a graph of the color rendering index and the total luminous flux with respect to the concentration is obtained.
From the graph, the density that maximizes the color rendering is obtained. If the color rendering properties and the total luminous flux satisfy the desired conditions, and there are two densities that achieve this, a lower density is selected.

Further, in the above embodiment, LEDs of three colors of red, green and blue are used. However, white light can be produced by two colors of red and blue green or yellow and blue. Such a white LED light source composed of two-color LEDs is easily put into practical use because an appropriate organic dye can be economically adjusted and used. Of course, there are two types of LED chips, which is more convenient. Further, not only the epoxy resin but also other thermosetting resins that are preferably transparent can be used for the wavelength conversion member. These thermosetting resins are heat-resistant, lightweight, and inexpensive.

As in the light source 20 shown in FIG.
Reflection cup (or reflection plate) outside 3, 24, 25
22 and a wavelength conversion member 27 at a distance therefrom.
The light source 20 can be reduced in cost and its performance can be improved. It is obvious that the embodiment of the present invention can be applied to the light emitting elements 23, 24 and 25 other than the LED chip. For example, if the outer tube and cover of a conventional HID lamp are made of plastic and an organic dye is dissolved and dispersed in plastic, the color rendering properties can be easily improved.

[0024]

As described above, the above objects can be achieved by implementing the present invention.

[Brief description of the drawings]

FIG. 1A is a schematic plan view of a conventional white LED light source.

1B is a cross-sectional view of the LED light source of FIG. 1A along AA.

FIG. 2 is a graph showing a relative spectral distribution of a conventional white LED light source.

FIG. 3 is a graph showing the absorption spectrum distribution of the organic dye rhodamine 19 (wavelength on the horizontal axis, relative absorbance on the vertical axis).

FIG. 4 is a graph of a relative spectral distribution showing an emission spectrum distribution of the organic dye rhodamine 19 (wavelength on the horizontal axis, relative energy on the vertical axis).

FIG. 5 is a sectional view corresponding to FIG. 1B of the LED light source according to the embodiment of the present invention.

6 is a graph of the relative spectral distribution of the LED light source shown in FIG. 5 (horizontal axis wavelength, vertical axis relative energy).

FIG. 7 is a sectional view corresponding to FIG. 1B of the light source according to the embodiment of the present invention.

[Explanation of symbols]

 1, 10, 20 White LED light source 2, 22 Reflection cup 3, 4, 5 LED chip 6 Epoxy resin dispersed with rhodamine 19 23, 24, 25 Light emitting element 27 Thermosetting resin dispersed with organic dye

Claims (5)

[Claims] 1. A light source for generating illumination light by additively mixing light from a plurality of light emitting elements that generate different light,
A light source, comprising: a wavelength conversion member including an organic dye for converting light from at least one of the light-emitting elements in the illumination light, whereby the color rendering of the illumination light is improved by the conversion. 2. The light source according to claim 1, wherein the wavelength conversion member includes an epoxy resin in which an organic dye is dissolved. 3. The light source according to claim 1, wherein the organic dye is rhodamine-based. 4. The light source according to claim 1, wherein the light emitting element is a light emitting diode chip. 5. The light-emitting device according to claim 1, wherein said wavelength conversion member is disposed apart from said light-emitting element.
The light source according to 1.