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APPLICATION OF CERAMIC COVER IN LED LIGHT MIXTURE

IP.com Disclosure Number: IPCOM000202043D
Publication Date: 2010-Dec-02
Document File: 4 page(s) / 65K

Publishing Venue

The IP.com Prior Art Database

Abstract

A technique to obtain uniform color appearance in LED is described. Phosphor coating in LED chip is not uniform and hence, there is angular color separation in LED, due to which, the color appearance is not uniform. The present technique introduces a ceramic cover to make the color appearance uniform.

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APPLICATION OF CERAMIC COVER IN LED LIGHT MIXTURE

BRIEF ABSTRACT

            A technique to obtain uniform color appearance in LED is described.  Phosphor coating in LED chip is not uniform and hence, there is angular color separation in LED, due to which, the color appearance is not uniform.  The present technique introduces a ceramic cover to make the color appearance uniform.

KEYWORDS

            LED, phosphor coating, ceramic cover, light emitting diode, angular color uniformity, reflector, translucent ceramics, crystal lattice, color separation

DETAILED DESCRIPTION

LED’s are used in a wide range of industries including LCD monitors or LCD televisions, general lighting applications, beamers, direct view applications, etc.  It is well known in the art that light of a first (peak) wavelength can be converted into light of a longer wavelength using a process known as luminescence/fluorescence.  The fluorescent process involves absorbing the light having the first wavelength by a wavelength-converting material such as a phosphor, exciting the luminescent centers of the phosphor material, which emit the light of the longer wavelength.  This process is used, for example, in LED’s to generate white light, wherein emission from a blue LED chip is partly converted to yellow/orange by an overlying phosphor layer, whereby unconverted blue light and converted yellow/orange light mix to white light.

However, a problem in conventional illumination systems comprising phosphor particle powders is that they cannot be used for many applications because they have a number of drawbacks: Firstly, the deposition of a phosphor particle layer of uniform thickness is difficult.  The phosphor particles tend to agglomerate, and hence, providing a uniform phosphor layer with particles of a known grain size is difficult.  Hence, the phosphor coating in LED chip is not uniform, and hence light with different color, in different angle emitted from LED, will be directly reflected by reflector.  Therefore, angular color separation takes place and the color appearance of the LED is not uniform. Especially for reflector lamp, angular color separation is about 14 SDCM (Standard Deviation of Color Matching), which is not acceptable by American National Standards Institute (ANSI).  


         Secondly, conventional phosphor particles are transferred into phosphor layers that backscatter a large part of the light emitted by the LED back into the chip, which is relatively absorptive, leading to lower light-extraction efficiency.

Conventionally, efforts have been made to modify the curve of reflector before LED.  However, the problem with conventional techniques is that the reflector curve gets very complicate and cost of reflector also increases simultaneously. Further, with the complicate reflector, angular color separation decreases only from 14 SDCM to about 7 SDCM, which is not acceptable by standards of ANSI.

Hence, there is an un...