lighting: Contemporary Lighting Technology

Contemporary Lighting Technology

The search for efficient artificial lighting during the 20th cent. first focused on improving incandescent lamp technology and high-intensity discharge (HID) lamps. The tungsten-halogen lamp, often called a halogen lamp, like the other incandescent lamps uses a tungsten filament as the light source, a gas filling that includes a halogen, and a quartz bulb. The halogens help preserve the filament and prevent lamp walls from darkening as quickly as those of the other incandescent lamps by causing the tungsten that evaporates during lighting to be redeposited on the filament instead of the bulb; more light is thus available to the task or work surface.

HID is the term commonly used to designate four distinct types of lamps—mercury vapor, metal halide, high-pressure sodium, and low-pressure sodium—that actually have very little in common. The mercury vapor lamp produces light when the electrical current passes through a small amount of mercury vapor. The color rendering qualities of the mercury vapor lamp are not as good as those of incandescent and fluorescent lamps. The metal halide lamp is similar to the mercury vapor lamp, the major difference being that the metal halide lamp contains various metal halide additives in addition to mercury vapor. The efficiency of metal halide lamps is twice that of mercury vapor lamps. Some of the newer metal halide lamps provide color similar to that of incandescent lamps while others emulate daylight. The high-pressure sodium (HPS) lamp has the highest lamp efficiency of all lamps commonly used indoors. It produces a golden-white light when electricity passes through a sodium vapor. The low-pressure sodium (LPS) lamp, the most efficient of all, is used where color is not important because all colors illuminated by an LPS light source appear as tones of gray or yellow.

The most promising technology is that of the light-emitting diode (LED). A tiny semiconductor microchip, an LED consumes little power, is long lasting, and is relatively inexpensive. It produces visible or infrared light when subjected to an electric current. First demonstrated in 1962 and appearing in a commercial product in 1968, LEDs were limited to small applications until 1985, when more powerful LEDs were produced. Their major limitation was that only red and green microchips were possible. In 1993 researchers at several universities in the United States and Japan developed an LED that produced blue light, which in conjunction with the red and green chips could produce white light. This made the LED a major player in illumination technology, and LED lightbulbs that can replace incandescent and compact fluorescent ones have been developed. The discovery of organic light-emitting diodes (OLEDs), made with plastics rather than silicon and other traditional semiconductor materials, opened the door for many specialty applications under the mantle of solid-state lighting. LEDs also offer the possibility of adjustable colors, permitting the use of lighting that enhances alertness during the daytime and aids sleeping during the nighttime, or that enhances different aspects of crop growth during a plant's life cycle.

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