Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With reflector – opaque mask – or optical element integral...
Reexamination Certificate
2002-08-22
2004-05-18
Wille, Douglas (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With reflector, opaque mask, or optical element integral...
C257S095000, C313S486000
Reexamination Certificate
active
06737681
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application is to apply for the priority insistence by the assumption of laid open patent JP 2001-251,407 and JP 2001-251423 basic.
The present invention relates to a light emitting device, particularly to a device that can emit uniform light with less color heterogeneity, for example, white light of high output power.
2. Description of the Related Art
Portable electronic devices, sign lamps, indication lamps and other devices are increasingly employing semiconductor light emitting elements, for example, light emitting diode (LED), that have high luminance and low power consumption, as the light sources. When such a semiconductor light emitting element is used to constitute a light emitting device, light emitted by the semiconductor light emitting element that is a point light source must be converted into planar emission of light.
Prior art of achieving planar light emission includes such techniques as a film that contains a light diffusion agent and is mounted in front of a semiconductor light emitting element chip, a lens that is mounted in front of a semiconductor light emitting element chip to control the directivity of light, and an array of semiconductor light emitting element chips arranged with a high density so as to provide quasi planar light emission.
However, the film including the light diffusion agent results in a low light transmissivity due to the light diffusion agent, while the technique using the lens or high density array results in higher manufacturing cost.
On the other hand, it has been proposed to form a reflector around a semiconductor light emitting element so as to reflect a part of the light from the semiconductor light emitting element forward, thereby achieving planar light emission.
Recently, the emission of white light have been increasingly demanded. Devices for emitting white or near white light are often made by using a semiconductor light emitting element that emits blue light and a YAG series fluorescent substance (yttrium aluminum garnet) dispersed in a sealing resin, so that a part of the light from the semiconductor light emitting element is absorbed by the fluorescent substance that in turn emits yellow light through wavelength conversion, and the blue light and the yellow light are blended so as to produce white light.
With this method of mixing the YAG series fluorescent substance in the sealing resin, uniform white light with less color heterogeneity can be produced, although light transmissivity through the sealing resin is lowered by the fluorescent substance, thus making it difficult to achieve a satisfactory optical output power.
In order to overcome such drawbacks, many variations of method of coating a reflector with a YAG series fluorescent substance have been proposed (see Japanese Unexamined Patent Publications (Kokai) No. 10-112557 (1998), No. 10-319877 (1998) (div. No. 2000-81847), No. 11-87778 (1999) (div. No. 2000-82849), No. 11-274572 (1999)).
However, with the structures that have been disclosed in the above patent publications so far, light emitted from the side faces of the semiconductor light emitting element has not been fully utilized.
Also with the structures disclosed in the above patent publications, there is such a problem that light is not fully diffused in a cavity that houses the semiconductor light emitting element, thus resulting in the emission of white light having color heterogeneity with the semiconductor light emitting element emitting bluish light and the reflector emitting yellowish light.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a light emitting device that can emit uniform white light with less color heterogeneity and high output power.
The light emitting device of the invention comprises a semiconductor light emitting element emitting at least part of light from side faces thereof; and a fluorescent member provided at a distance from the semiconductor light emitting element; the fluorescent member being capable of emitting light by wavelength-conversion due to absorption of part of light emitted from the semiconductor light emitting element and including at least yttrium aluminum garnet fluorescent substance as a component having at least one element selected from the group consisting of Y, Lu, Sc, La, Gd and Sm, at least one element selected from the group consisting of Al, Ga and In, at least Ce and at least one element selected from the group consisting of Pr, Sm, Cu, Ag, Au, Fe, Cr, Nd, Dy, Ni, Ti, Tb and Eu; wherein the fluorescent member has a first portion at a first distance from the semiconductor light emitting element and a second portion at a second distance farther than the first distance from the semiconductor light emitting element and the first portion has a higher efficiency of absorption of light emitted from the semiconductor light emitting element than that of the second portion.
Using the above fluorescent substance allows the color of light to obtain high color rendering properties.
In addition, designing the higher efficiency of absorption of light emitted from the semiconductor light emitting element at each portion of the fluorescent member as the portion being at the shorter distance from the semiconductor light emitting element, allows the light emitted from the side faces of the semiconductor light emitting element to be utilized more efficiently. Thus, the ratio in quantity of light wavelength-converted by the fluorescent substance out of light irradiated from the light emitting element becomes substantially uniform over the whole fluorescent member, thereby light of uniform color with high color rendering properties and less color heterogeneity can be emitted.
The light emitting device of the invention also comprises a semiconductor light emitting element emitting at least part of light from side faces thereof; and a fluorescent member provided at a distance from the semiconductor light emitting element; the fluorescent member being capable of emitting light by wavelength-conversion due to absorption of part of light emitted from the semiconductor light emitting element; wherein the fluorescent member has a first portion at a first distance from the semiconductor light emitting element and a second portion at a second distance farther than the first distance from the semiconductor light emitting element and the first portion has a higher efficiency of absorption of light emitted from the semiconductor light emitting element than that of the second portion.
With this constitution, designing the higher efficiency of absorption of light emitted from the semiconductor light emitting element at each portion of the fluorescent member as the portion being at the shorter distance from the semiconductor light emitting element, allows the light emitted from the side faces of the semiconductor light emitting element to be utilized more efficiently. Thus, the ratio in quantity of light wavelength-converted by the fluorescent substance out of light irradiated from the light emitting element becomes substantially uniform over the whole fluorescent member, thereby light of uniform color with high color rendering properties and less color heterogeneity can be emitted.
According to the invention, it is preferable that the fluorescent member is formed of a transparent resin material with a fluorescent substance dispersed therein, and said efficiency of absorption is changed continuously or stepwise correspondingly to the absolute quantity of the fluorescent substance.
The efficiency of absorption at each portion of the fluorescent member is adjustable continuously or stepwise by changing the absolute quantity of the fluorescent substance continuously or stepwise.
According to the invention, it is preferable that the first portion has a higher density of the fluorescent substance in the fluorescent member than that of the second portion.
The efficiency of absorption at each portion of the fluorescent member is also adjustable continuously or stepwise by changing the density of the fluorescent
Morrison & Foerster / LLP
Nichia Corporation
Wille Douglas
LandOfFree
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