Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2003-02-20
2004-04-06
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S500000, C313S312000, C362S800000
Reexamination Certificate
active
06717362
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to Light Emitting Diodes (LEDs) and, in particular, to an LED with an improved light extraction capability.
BACKGROUND ART
A Light Emitting Diode (LED), as with other diodes, consists of a p-n junction that allows current to flow in one direction only. However, when a positive bias electrical voltage is applied to the LED, light is emitted in the form of photons.
LEDs are more durable than conventional incandescent bulbs, because LEDs do not have filaments that can bum out. However, the main advantage of LEDs, when compared with conventional incandescent bulbs, is their efficiency. In conventional incandescent bulbs the light producing process involves generating a lot of heat, which is wasted energy if the purpose is to generate light. In contrast thereto, LEDs generate relatively little heat, causing more of the energy supplied to the LED to be converted to light.
FIG. 1
illustrates the structure of a typical prior art LED
200
. Energy is supplied to the p-n junction
210
through two terminal pins
230
and
231
, causing the p-n junction to emit light. The p-n junction
210
of the LED
200
is encapsulated in a package
220
, which is transparent to the light emitted from the p-n junction
210
. For the light generated by the p-n junction
210
to be visible, the photons emitted by the p-n junction
210
have to travel through the package
220
, and then through air to the eyes of an observer. In order to optimise the efficiency of the LED
200
, it is desirable for as much as possible of the light generated by the p-n junction
210
to be emitted from the LED
200
to the observer. The invention seeks to address this desirable result.
U.S. Pat. No. 5,777,433 addresses this desirable result by providing a high refractive index package material for use in manufacture of the package
220
. The high refractive index package material includes a host material and nanoparticles held in the host material. The host material has a refractive index lower than that of the p-n junction
210
, and is transparent to the light emitted from the p-n junction
210
. The nanoparticles are formed from a material having a refractive index higher that that of the host material. The resulting high refractive index package material has an effective refractive index that is higher than that of the host material without decreasing the transparency of the high refractive index package material. As will be shown herein, LEDs formed from the high refractive index package material disclosed in U.S. Pat. No. 5,777,433 have a limited success in achieving the desirable result.
SUMMARY OF THE INVENTION
According to an aspect of the invention, there is provided a light emitting diode comprising:
a p-n junction diode for emitting light; and
a transparent casing encapsulating the p-n junction diode, the transparent casing having an inner portion in contact with the p-n junction diode, wherein the refractive index of the transparent casing is higher at the inner portion than an outer portion thereof.
In one embodiment, the transparent casing comprises at least a first and a second transparent layer, with the first transparent layer encapsulating the p-n junction diode, and the second transparent layer encapsulating the first transparent layer. The refractive index of the first transparent layer is higher than the refractive index of the second transparent layer.
In another embodiment, the transparent casing comprises at least one transparent layer, where the refractive index of the transparent layer is higher at an inner portion thereof than an outer portion.
The effect of the different refractive index arrangement of the layers is to reduce the Fresnel loss experienced by light emitted from the p-n junction diode.
REFERENCES:
patent: 5777433 (1998-07-01), Lester et al.
patent: 5813753 (1998-09-01), Vriens et al.
Chin Yee Loong
Goh Kee Siang
Lee Boon Kheng
Tan Chen Why
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