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5. Repercussion effects
Completing the light spectrum for semiconductor devices has been accomplished through the development of the blue LED and LD, which, together with red and green devices, enables various kinds of applications.
GaN is now used as a key material for producing ultraviolet, blue, green and yellow light emitting devices by changing the indium doping content. Of special importance, green LEDs with higher purity and higher efficiency than that of GaP-based LEDs have already been developed as commercial products using indium doped GaN.
The development of the blue LD has enabled the development of the next generation of large-capacity optical storage discs. Nine electronics manufacturing companies from Japan, Korea, and Europe recently announced the specifications for the next generation of CDs/DVDs, known as the "Blu-ray Disc," in February 2002. The blue LD will enable 12 cm discs to record, rewrite, and play back 27 gigabytes (GB) of data - six times more information than on a conventional disc. This will allow for the recording of all kinds of digital content (audio, video, television, photographs, etc.) delivered to homes and offices through digital broadcasting and broadband communication. The recording of two hours of digital high-definition video and thirteen hours of standard TV broadcasting will be possible with the Blu-ray Disc. In addition, double-sided discs or the enlargement of the size of the disc is also possible, enabling one disc to store 50 to 100 GB data. One terabyte recording becomes possible using multiple discs. Large projection displays can be designed using all three colors of LDs.
Using blue LEDs in conjunction with red and green LEDs, large outdoor full-color displays, which are clear and easy to see even in bright sunlight, have been developed and displayed on buildings.
LEDs have also been increasingly used to replace incandescent bulbs in traffic signals. LEDs have many advantages over conventional lamps. First, the light provided by LEDs is clearer, especially in direct sunlight. Second, the lifespan of LEDs is over eight years, much longer than that of incandescent lamps with average lifespans of six months to one year. Thirdly, LEDs reduce electric power consumption by one-fourth. The Department of Transportation in California replaced 200,000 traffic signals with LEDs during the most recent energy crisis. There are about one million traffic signals for cars and 770,000 for pedestrians in Japan. In about 8,000 of these signals, incandescent bulbs have been replaced with LEDs at present. It is estimated that when all traffic signals for pedestrians are replaced with LEDs, electric power consumption will be greatly reduced and carbon dioxide gas generation will fall by 110,000 tons per year21).
There are two types of white LED. One uses the blue LED combined with a yellow fluorescent substance. The other consists of blue, green and red LEDs. Both types of white LED were enabled by the development of the blue LED22). In the near future, the efficiency of the white LED should be improved to generate five times better efficiency than the incandescent lamp and the same efficiency as that of fluorescent light (50%). The lifespan of the white LED is over 8 years, which is much longer than the one-year durability of the white incandescent lamp and the fluorescent lamp. When the use of white LED lightning is expanded to all kinds of living spaces, it is expected to contribute greatly to the reduction of electric power consumption through the high efficiency of its light emission, and to the reduction of waste through its longer life. White LED lighting is flexible in terms of shape (flat, curved, spherical) and color (changeable tone by controlling the three colored LEDs respectively). The flexibility of this type of lighting is ideal and contributes to improving living environments.
The total market size of blue and white LEDs was estimated to be 90 billion yen in 2001 and is expected to grow to 230 billion yen in 200623). When the white LED lightning replaces the incandescent bulb and the fluorescent lamp, the market size is expected to grow to more than one trillion yen. As for the blue LD, the market size of the market for blue LDs will benefit greatly from the development and commercialization of the next-generation, high-density CD/DVD, growing to more than several tens of billion yen24).
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