Tungsten halogen lamps, commonly called just halogen lamps, are incandescent lamps specially designed to burn hotter and brighter. They are great for places where bright light and tight focusing are desired. They are known for their compact size, high efficiency, long life, good color rendition and excellent light-output over their lifetime.
The light output from an incandescent lamp depends on the temperature of the filament. The hotter the filament becomes the more energy is released in the form of visible light. Halogen lamps are designed to be a bulb inside a bulb. The primary bulb or capsule encloses the filament and its fill gas. This capsule is coated with a special film on the inside part of the glass that reflects infrared radiation and allows visible light to pass through.
For standard incandescent lamps, almost 90% of the energy consumed by the lamps is released in the form of heat. Some of this heat is actually infrared radiation. The infrared or "IR" coating on the halogen lamp reflects this infrared radiation back onto the filament making it burn hotter producing more and brighter light.
Halogen lamps are also designed to reduce the degenerative process by which tungsten metal evaporates off of the filament wire. In halogen lamps, the evaporated tungsten metal is redirected back to the filament and thus the filament "rebuilds" itself as it burns. This results in a longer rated life for halogen lamps over standard incandescent lamps.
The capsule in the halogen lamp is normally enclosed in an outer bulb. This prevents much of the heat from transferring to the environment while also serving as a safety shield if the halogen capsule ruptures or explodes.
Low Voltage Halogen
A special class of low voltage halogen lamps has become popular in homes for accent and kitchen lighting. It is characterized as having very high light output and a sharply defined and well controlled beam spread.
The low voltage halogen lamps are available primary in the miniature reflector called "MR" designs. Since they operate at low voltage they do require a special transformer. A common configuration is a track that attaches to the ceiling, wall or sometimes even the floor, where the heavy transformer "head" containing the lamps can be moved back and forth, adjusted or aimed, and even removed.