Why do low-energy light bulbs contain mercury?
It’s essential to the way they work. Compact fluorescent lightbulbs (CFLs) are tubes containing mercury and noble gases (typically argon). When the bulb is switched on, electrons stream from a tungsten-coated coil. They collide with mercury atoms, exciting their electrons and creating flashes of ultraviolet light. A phosphor coating (typically composed of metal oxides or phosphates) on the inside of the tube absorbs this light and re-emits it at visible wavelengths. This is also how fluorescent strip lights work. How much mercury do CFLs contain? Up to 5 milligrams – a tiny amount when compared to the 3 grams in a mercury thermometer, says Adrian Westwood, from the UK Environment Agency. Fluorescent strip lights contain similarly tiny amounts, reduced from the 100 milligrams present in first-generation CFL bulbs. Couldn’t we do without mercury in household lighting? Not in a fluorescent light. Light-emitting diodes (LEDs) don’t contain mercury, but they’re still costly, and researchers
