A halogen bulb is a type of incandescent light bulb, introduced in 1958. The halogen bulb is capable of burning much more brightly than conventional light bulbs, and it is a popular choice for headlights and other applications for which very bright light is needed. In addition to burning more brightly, halogen bulbs are also more efficient and have a longer life expectancy than conventional light bulbs.
The halogen bulb uses a design very similar to that of conventional light bulbs, consisting of a tungsten filament enclosed in another material. The halogen bulb uses quartz instead of glass, however, allowing the bulb to be much smaller because quartz can withstand higher temperatures than glass and therefore may be positioned much closer to the filament. In addition, halogen bulbs use halogen gases, instead of argon or nitrogen, two gases commonly used in conventional light bulbs.
A light bulb works by applying electricity to the tungsten filament, which heats up and puts out light. However, as the filament heats, it also begins to break down the tungsten, which begins to collect inside the bulb, often leaving dark deposits. Ultimately, the filament will break at a weak point, causing the light bulb to burn out.
Any surface contamination, notably the oil from human fingertips, can damage the quartz envelope when it is heated. Contaminants will create a hot spot on the bulb surface when the bulb is turned on. This extreme, localized heat causes the quartz to change from its vitreous form into a weaker, crystalline form that leaks gas. This weakening may also cause the bulb to rapidly form a bubble, thereby weakening the bulb and leading to its failure or explosion, and creating a safety hazard. Consequently, manufacturers recommend that quartz lamps should be handled without touching the clear quartz, either by using a clean paper towel or carefully holding the porcelain base. If the quartz is contaminated in any way, it must be thoroughly cleaned with alcohol and dried before use.
Halogen bulbs come with a few cautions. Like regular light bulbs, halogen bulbs get hot. Because the quartz envelope is so close to the filament, however, halogen bulbs get much hotter than conventional bulbs and can cause burns if handled. A halogen bulb can also start a fire if it is used near drapery or other flammable objects. In addition, handling a halogen bulb with bare hands exposes the quartz to salts and oils in the hands and may cause a weak point. This will decrease the life of the bulb, and it is recommended that halogen bulbs be handled with gloves or cloth to prevent unnecessary contact, and wiped down if they are handled.