White light LED

Toshiba is set to launch a white light emitting diode (LED) that points the way to a stable white light source with the luminosity required for the future replacement of incandescent lamps.

The new device was jointly developed with Toyoda Gosei and the two companies will commercialise and market it independently. Samples will be available from April 2001, and mass production will start from November 2001.

The new LED integrates Toshiba’s phosphors and packaging with Toyoda’s LED, which achieves a short peak wavelength approximately 380 nanometers (nm). The diode will be manufactured by Toyoda and packaged by Toshiba in a phosphor- mixed transparent resin package. Both companies will market the product under their own brand name.

The white LED holds out great promise as a high luminosity, low power consumption light source. While the main goal is a level of luminosity allowing replacement for incandescent lamps, current applications include the instrument panels of motor vehicles and LCD backlighting.

The new LED adopts a technological approach differing from that used in conventional LEDs. Light emission in the visible wavelength band is controlled by excited phosphors, not by using temperature changes in the LED to achieve a change in colour output.

The fact that the LED emission does not directly determine the colour brings advantages in overall controllability and wavelength stability. Incorporated in LCD products, the new diode achieves improved tonic reproduction and enhanced colour durability during temperature shifts.

The new LED realises a short wavelength light source by reducing the indium in an indium-doped GaN emission layer. This excites red, green and blue phosphors in the transparent resin of the device package to output white light.

The RGB balance of the phosphor layer determines the output colour, and different coloured output can be achieved through modified phosphor balance. The emission light from the LED itself does not directly contribute to the white colour.

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