Energy-saving light bulb, X-ray. This is a form of fluorescent lighting. This bulb comprises a glass bulb enclosing three fluorescent tubes (U-shaped). The tubes draw electrical power through two metal contacts (bright spots, bottom left). This sets up an electrical voltage that ionizes the inert gas (usually argon) inside the tubes. A small amount of mercury in the tubes is vaporized as the bulb heats up. The mercury atoms absorb energy and lose it by emitting ultraviolet (UV) light. The tubes are coated in phosphor, which absorbs the UV light and then emits visible light. More energy converts into light instead of heat, and such bulbs are 4-6 times more efficient than a filament light bulb.