Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1999-06-21
2002-01-08
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S499000, C257S461000, C257S607000
Reexamination Certificate
active
06337536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a white color light emitting diode (LED) which can produce white light by a single LED chip and further relates to a neutral color LED which can make redpurple light or pink light which is a neutral color between red and blue by a single LED. In particular, this invention is directed to the structure of the white color LED and the neutral color LED. White light is an assembly of a plurality of wavelengths including blue, red, green or so. There is a strong desire for a new light source of white. White light is most suitable for illuminating light sources, since white light includes all primary colors. White light is appropriate for various displays. White light is also used for the backlight of liquid crystal displays (LCD). Neutral tint LEDs between red and purple are also suitable for displays and illumination. This invention proposes the neutral color LED and the white color LED suitable for illumination, displays, LCD backlight and so forth.
This application claims the priority of Japanese Patent Application No. 10-194156(194156/1998) filed on Jul. 9, 1998, Japanese Patent Application No. 10-316169(316169/1998) filed on Nov. 6, 1998 and Japanese Patent Application No. 10-321605(321605/1998) filed on Nov. 12, 1998 which are incorporated herein by reference.
2. Description of Related Art
An LED produces light by lifting electrons by a current and throwing down the electrons over the band gap (forbidden band) between a valence band and a conduction band. The electron transition energy generates light. The band gap is equal to the energy of a photon which is a quantum of light. The band gap of an active layer gives the wavelength of the emitting light. The wavelength determines the color of the light. The color of the light depends upon the material of the active layer of an LED.
All the conventional LEDs have utilized only the electron band gap transition for making light. All the band gap transition LEDs emit monochromatic light (monochromatic LEDs). Monochromatic LEDs of emitting red, yellow, green or blue color have been produced and sold. For example, red light high luminescent LEDs which produce stronger power than several candelas (Cd) have been put on sale. The red light LEDs are based upon active layers of aluminum gallium arsenide (AlGaAs) or gallium arsenide phosphide (GaAsP). Inexpensive red light LEDs have wide scopes of applications. Green/yellowgreen light LEDs having a gallium phosphide (GaP) light emitting layer (active layer) have been manufactured and sold, too. Blue light LEDs including an SiC layer as an active layer have been proposed. Blue/green light LEDs based on an active layer of gallium indium nitride (GaInN) have been on market. LEDs having an AlGaInP active layer are orange/yellow color LEDs. Monochromatic LEDs having the following combinations of the colors and the active layers have been manufactured.
Colors
Materials of active layers
(1) red LED
AlGaAs, GaAsP
(2) green-yellowgreen LED
GaP
(3) blue LED
SiC
(4) blue-green LED
GaInN
(5) orange-yellow LED
AlGaInP
These are already matured as inexpensive practical LEDs. Among these LEDs, GaP LEDs and SiC LEDs have not attained to higher power emission than one candela, because GaP and SiC are indirect transition type semiconductors. What determines the wavelength is the material of the active layer. Such a crystal, that has a desired band gap and satisfies conditions, for example, the lattice matching condition and so on, is selected as an active layer.
All the conventional LEDs can make a single color, because the LEDs make use of the photon emission induced by the band gap transition of electrons. Thus, the conventional LEDs are all monochromatic light sources. Monochromatic LEDs have wide scope of utility for displaying light sources. However, monochromatic LEDs cannot replace all the current light sources. Monochromatic light is impotent to use lighting (illumination), special displays or LCD backlight, since the monochromatic light includes only the light having a single wavelength. If a monochromatic LED were used for a lighting source, illuminated objects would all wear the color emitted from the monochromatic LED instead of the inherent color of the objects. If a monochromatic LED were employed for LCD backlight, the LCD would show monochromatic images of the color.
Lighting or illuminating requires white color light sources which inherently include all primary colors and neural color light sources which include neutral colors between purple and red. However, there have been no semiconductor LEDs capable of emitting white light yet. Illuminating light is still supplied by incandescent light bulbs or fluorescent lamps in general. Although being cheap, incandescent light bulbs are suffering from a short lifetime and a low luminous efficiency. Fluorescent lamps also suffer from a short lifetime, though they enjoy a higher luminous efficiency than the incandescent light bulbs. Further, the fluorescent lamp requires heavy accessories, e.g. voltage stabilizers. The fluorescent lamps have further the drawbacks of a big size and a heavy weight.
It is hoped that future white and red-purple neutral color light sources satisfy the attributions, that is, small size, simple accessories, long lifetime, high luminous efficiency and low price. One candidate capable of sufficing these difficult requirements would be a semiconductor light emitting device (LED or LD). LEDs are small, light and inexpensive light sources having a long lifetime and high efficiency. However, since LEDs utilize electron transitions across the forbidden gap between the valence band and the conduction band, the LEDs inherently emit monochromatic light. Neither single LEDs nor single LDs can generate white color light due to the electron band gap transition emission. Monochromaticity is the inherent property of LEDs.
With regard to neutral colors, the conventional LEDs can make primary colors (RGB) and restricted neutral colors. The colors the current LEDs can produce are red, orange, yellow, yellowgreen, green, bluegreen, blue, bluepurple and purple. Among them, red, green and blue are primary colors. Orange, yellow and yellowgreen are neural colors between red and green. Bluegreen, bluepurple and purple are neutral colors between blue and green. Among three primary colors, red has the longest wavelength, green has a middle wavelength and blue has the shortest wavelength. Blue and green are a nearer pair. Green and red are another nearer pair. LEDs can make neutral colors between two neighboring primary colors (R-G and G-B). Any neutral colors of the conventional LEDs are still monochromatic colors which possess only one wavelength. Conventional LEDs basing on the band gap transition can produce monochromatic R-G or G-B neutral colors.
Any conventional LED can make neither neutral color between red and blue (R-B) nor neutral color among red, green and blue (R-G-B). Red and blue have very different wavelengths. Neutral colors between blue and red (B-R) and among blue, red and green (P-G-B) are no more monochromatic colors having a single wavelength but complex colors including a plurality of wavelengths. Thus, the white (R-G-B) color and the R-B neutral colors cannot be produced by the electron band gap transition in principle.
Instead of monochromatic light sources, lighting, ornament or display requires neutral colors being a mixture of red and blue and white color being a mixture of blue, green and red. Conventional LEDs utilizing the electron band gap transition are all monochromatic light sources. Although the conventional bluegreen LEDs, bluepurple LEDs and orange LEDs are essentially monochromatic LEDs, each LED has only one peak of wavelength somewhere in the emission spectrum.
The neutral color in the present invention does not mean a monochromatic color intervening between two primary colors but a mixture of primary colors. Monochromatic light source has a single peak in the spectrum. But, the neutral color of the present invention has at least
Katayama Koji
Matsubara Hideki
Takebe Toshihiko
Guharay Karabi
Patel Nimeshkumar D.
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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