Halogen lamps have been around for a long time and they remain a popular choice in a wide range of different applications. Although they are available in many different formats, they all work on the same principle, in which a tungsten filament is heated due to its resistance, in the same way as an incandescent auto bulb. In the halogen lamp, however, the filament is enclosed by a halogen gas, usually iodine, mixed with an inert gas such as krypton or Xenon. This results in a tungsten/halogen reaction in which an intense white light is emitted. Vaporised tungsten is then re-deposited on the filament resulting in the bulb envelope remaining clean, and longer bulb life. This reaction does result in very high temperatures and halogen bulbs invariably get hot. Common applications include security floodlights, downlighters and domestic lamps. They are also available in many traditional socket types as direct replacements for incandescent bulbs, over which they offer substantial energy savings. The main drawback of halogen lamps is their tendency to become very hot, requiring appropriate mountings, while the new generation of LED lamps are now available in almost every possible configuration, emit little heat and offer greater energy savings.