Hitachi Cable News Vol.354 ::: The "Light" of the 21st Century Will Change Society [Part1]

General lighting, neon signs, electronic signboards, traffic signals, hazard lights...various kinds of artificial lights are ubiquitous in our daily lives. The most common electric light sources today remain bulbs and fluorescent lamps, but another light source has recently been infiltrating many fields at a rapid pace: the LED, or light-emitting diode.
Take the traffic signals -- indispensable for road safety -- as an example. Have you noticed an increase of late in the number of traffic signals clearly visible even in the afternoon sunlight? More and more conventional bulb-based signals have been replaced by LED-based signals in the past few years (see inset), and LEDs are increasingly used in electronic signboards often found at train stations and on the street. The higher-definition displays achieved by LED light sources allow brighter and clearer destination screens on train platforms than the previous reflective screens. LED-based signboards are used in many other applications as well, including store billboards and large displays at stadiums.

Why are LED-based signals clearer?

Conventional bulb-based signals transmit their light through red-, green-, and yellow-tinted lenses to provide colored signals.
Reflection of direct sunlight by these lenses causes signals to appear lit when they are actually not, a phenomenon called "pseudo-lighting," which makes it difficult to determine which signal is lit in the afternoon sunlight. With LED-based signals, however, LED lamps themselves emit colored lights, eliminating the need for tinted lenses and preventing pseudo-lighting.Furthermore, LEDs are increasingly finding use in photo-sensors of color copiers, scanners, and laser printers.

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