The Japanese are working on LEDs as incandescent bulb replacements

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A group of researchers at Nicia Corporation set out to design LEDs that could replace incandescent light bulbs. To this end, they developed highly efficient white LED lighting, which has a wide range of applications.

The researchers claim with their white LEDs achieve a luminance efficiency approaching the theoretical maximum. This efficiency, which is measured in lumens per watt, is 260 to 300 lumens per watt for white LEDs. The white LEDs developed by the Nichia researchers led by Yukio Narukawa achieve efficiencies of up to 265lm/W at a current of 5mA and 249lm/W at 20mA. In comparison, commercially available white LEDs achieve about 150lm/W. Incandescent lamps stick at 16lm/W and fluorescent lamps reach about 100lm/W.

The light emitting diodes designed by the researchers may achieve high efficiencies, but their so-called luminous flux is relatively low at 14.4 lumens. That luminous flux is the brightness of the light source as perceived by the human eye. By adjusting the design, they were able to produce LEDs with higher luminous fluxes, at the expense of efficiency. For example, they made white LEDs with a luminous flux of 203 lumens with an efficiency of 183lm/W, and a version with 1913 lumens at 135lm/W. That amount of light is comparable to a 20W energy-saving lamp.

The LEDs were produced by applying a yellow phosphor coating to blue LEDs. The LED with a yield of 1913 lumens was made up of four semiconductors. The blue light from the LEDs is combined with yellow fluorescence and red phosphorus was added to balance the spectrum. The electrodes of the LEDs were also coated with indium tin oxide to reduce light absorption. The working voltage of the semiconductors was 2.8V. According to Narukawa, the high price of its LEDs would come down in the future and the LEDs could serve as a replacement for a broad spectrum of light sources.

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