Those lights that decorate the streets so gaily during Christmas Season are “Light-Emitting Diodes,” or LED. LED were developed in the United States in the 1960s, initially for use as indicator lamps in electrical appliances. During the 1990s, following the invention of the blue LED in Japan, LED applications expanded dramatically. As well, LED are undergoing continuous development as the lighting apparatus for the next generation. This report provides an overview of this new form of light.

1.Principle of Operation and Materials Used in LED
LED essentially consists of an active layer of semiconducting material sandwiched between p-type and n-type semiconductor cladding layers. When voltage is applied in the forward direction, electrons and electron holes flow into the p-n junction. When an electron meets a hole, the electron fills the hole and falls into a lower energy level, giving up energy in the form of a photon of light.

The LED developed in the 1960s emitted dark red and greenish-yellow light. With the development of a yellow LED in the 1970s and a blue LED in the 1990s, as mentioned above, the three primary colors of light became available, leading to the invention of a white LED later in the 1990s. With this invention, LED came to hold great promise as light sources for general lighting needs, a potentially large market.

Colors emitted by LED depend on the materials used for the LED. In other words, the materials forming the p-n junction determine the wavelength of the light emitted, therefore its color. The relations between materials and colors are shown below:

Among the above advantages, low power consumption contributes to environmental protection, one of the most important global issues of our time. To assess the energy efficiency of LED, a trial calculation was carried out. Total power consumption and carbon dioxide emission were calculated for comparison, assuming that incandescent lamps had been replaced with LED in all traffic signals throughout Japan.

If the incandescent lamps in all of the 1,950,000 traffic signals in this country (1,100,000 units for vehicles and 850,000 units for pedestrians) were replaced with LED, the amounts of energy saved and carbon dioxide emissions reduced would be as follows:

As described earlier, the invention of commercially viable blue LED led to the development of white LED technology for general lighting applications, opening up great possibilities for expanding the LED market. To expand the market, it may be necessary to overcome the following issues:

The industry expects that, after these issues have been resolved, LED will be in widespread use as general lighting apparatus, around 2015.

As mentioned previously, blue LED technology was developed in Japan. In 2001, the researcher who developed the blue LED filed a lawsuit against his former employer over the rights to the patent for blue LED production. This dispute ended in 2005, when the two parties accepted the settlement agreement mediated by the Tokyo High Court at the second hearing. This case is regarded as a milestone judgment relating to intellectual properties. In the settlement, the researcher’s total remuneration was reportedly some 840 million yen (whereas he claimed 20.1 billion yen). The figure was the highest sum ever paid for remuneration for an invention in Japan, suggesting that the potential of the blue LED was evaluated very highly.

In above figures, quantity is in millions of units, amount is in millions of Japanese yen.

(This report was compiled with reference to websites and other materials of the following organizations: “Japan LED Association” and “Matsushita Electric Works, Ltd”.)