Halogen light bulb. Coloured X-ray of a gooseneck halogen light bulb. Halogen light bulbs operate at much higher temperatures than normal domestic bulbs, enabling them to produce a more natural light balance. At top, three gooseneck glass tubes are filled with low-pressure iodine gas. This prevents fast depletion of the tungsten filaments (orange, at centre left and right). The iodine reacts with the tungsten atoms sublimating from the filament, preventing them from depositing on the glass. When the bulb is switched off, the tungsten is redeposited onto the filaments. Although this halogen light bulb is long-lasting, its high temperature is a greater fire hazard.