Traditional incandescent filament lamps are notoriously inefficient, much of the energy is dissipated as heat. This is important when it is recalled that 25% of the world’s electricity is used for lighting. Fortunately, by no means all of this electricity is used inefficiently in filament lamps. Fluorescent tubes play a major role, particularly in industry, commerce and street lighting.

There have been significant improvements in lighting in recent years. The light output of fluorescent tubes has been enhanced by the development of new phosphor coatings. Compact high-energy lamps are becoming commonplace; a 20-W lamp gives the same light output as a 100-W incandescent filament lamp and lasts much longer. If all the traditional filament lamps in the world were replaced by high-efficiency lamps, or by florescent tubes, there would be a massive saving in electricity. In the longer term, there are good prospects for light emitting diodes (LEDs) to replace conventional lighting, but this will necessitate substantial improvements in performance and reductions in cost. Already, red LEDs are used in some traffic lights and in brake lights on cars. With the advent of LEDs based on gallium nitride, which emit in the blue or green, the possibility exists of replacing all the hundreds of millions of traffic lights around the world with LEDs, to give large savings in electricity consumption. New advances in photochemistry and in photoelectrochemistry (see Section 5.6, Chapter 5) hold out the prospect of even more efficient forms of lighting.

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