- Halogen bulbs contain a tungsten filament that is surrounded by an inert gas mixed with a halogen. Halogens are a series of nonmetal elements that have a specific reaction to the presence of electricity. In a halogen bulb, the halogen gas (usually bromine or iodine) causes the tungsten particles that separate from the lit filament to eventually settle back on the filament. This prolongs the life of the bulb and prevents the particles from attaching to the glass casing, where, over time, they would block out a percentage of the light being emitted.
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Halogen bulbs can also operate at higher temperatures than standard incandescent light bulbs. This allows them to produce more light with the same amount of energy (or to supply the same amount of light while using less energy). Depending upon the application, the energy efficiency of a halogen bulb can outweigh the added cost relative to a standard incandescent, or even a florescent lamp.
When operated at a higher temperature, halogen bulbs also produce light with a hotter color temperature. This makes halogen bulbs a closer approximation to daylight than other types of electric lamps. - Halogen bulbs became common in automobile headlights in the early 1990s. These halogen bulbs offered whiter, brighter light than the bulbs used previously. Like all halogen bulbs, they also offered longer lifespans and greater efficiency. As soon as halogen bulbs became standard in most cars, automakers began seeking new alternatives to set their cars apart. High intensity discharge (HID) and xenon headlights were offered in some luxury and sports cars, using the same principles as halogen bulbs to produce even whiter, even blue-tinted, light.
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Halogen bulbs were first manufactured in the late 1950s by General Electric. Since that time they have seen use in a number of applications. Besides becoming the standard for automotive headlights in the 1990s, halogen bulbs are popular for stage lighting and in photography due to their ability to simulate the color temperature of natural sunlight. They are also used in some film and slide projectors, mainly for the intensity of the light they produce, which can produce a vivid projection over a great distance.
Halogen bulbs are also used in architectural applications, such as exterior building lighting. Here it is primarily their aesthetic appeal that is favored, casting a warm, "glowing" light. -
Halogen bulbs do have several distinct drawbacks that prevent their widespread use. Chief among these is their cost, which is higher than standard incandescent bulbs due to a more complex manufacturing process.
Additionally, halogen bulbs burn as very high temperatures, with some halogen filaments reaching 5000 degrees K. This makes them potential sources of fire or burns unless properly installed and operated. Halogen bulbs also produce light that contain dangerous ultraviolet (UV) rays and can actually cause a sunburn after prolonged exposure. Some halogen bulbs have special coatings to filter out much of the UV light.
