Page - 46 - in Water, Energy, and Environment - A Primer

filament lamps),buthedid invent the firstcommerciallypractical incandescent bulb. It was introduced into residential use more than 125 years ago. Its principal shortcoming is that more than 90% of the energy used by the traditional incandescent bulb escapes as heat and less than 10% goes into producing light. Filaments also burn out and are fragile, and a typical bulb lifetime is about 1000hours. Halogen lamps, also in common use today, are incandescent lamps with a little halogen gas (iodine or bromine) added to the bulb. The chemical reaction between the halogen and the tungsten wire allows the filament to operate at a higher temperature and increases the bulb’s lifetime and light-producing efficiency (also referred to as efficacy). A fluorescent lamp or fluorescent tube is a low-pressure mercury-vapor gas-discharge lamp that uses UV-stimulated fluorescence of a deposited phosphor to produce visible light. It is more energy efficient than an incandescent lamp, but does require an electrical ballast to regulate the current through the lamp, increasing its initial cost. CFLs fold a fluorescent lamp tube into the space of an incandescent bulbwith a ballast in the base. Theyuse3–5 times less energy than incandescent bulbs of the same light output and have much longer lifetimes. They do contain a small amount ofmercury, creating a disposal problem. Light-emitting diodes (LEDs) are solid-state semiconductor, monochromatic, point light sources. First appearing as practical electronic components in 1962, early LEDs emitted low- intensity red light, but modern versions are available at visible, ultraviolet, and infraredwavelengths with very high brightness. (Note: when different visible colors are mixed, white light can be produced). Today they are used in applications as diverse as aviation lighting, automotive lighting, advertising, general lighting, and traffic signals. They are also used in the infrared remote control units of many commercial products including televisions, DVD players and other domestic Water,Energy, andEnvironment–APrimer46