Halogen bulb illumination is produced when a tungsten filament is heated sufficiently to emit light. Halogen light bulbs use a fused quartz "capsule" allowing for higher temperatures. The "capsule" contains a vapor, originally iodine but now usually bromine. Halogen is the name given to the family of electronegeative elements including bromine, chlorine, fluorine and iodine. Halogen bulbs are referred to as "tungsten halogen", "quartz halogen" or "halogen".