Fluorescence and phosphorescence: Easier to investigate than to spell

摘要

Fluorescent lamps that use magnetic ballast (the cheapest you can get) flicker at twice the mains frequency (120 Hz or 100 Hz, depending on the country). Every time the sinusoidally changing voltage crosses zero value, the radiation of the mercury gas in these lamps drops significantly and so does the emission of the white powder coating (usually called phosphorus) on the inner surface of the glass tube. This phenomenon, i.e., the immediate emission of light by a substance that has absorbed light of other electromagnetic radiation, is called fluorescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed light. If the source of primary light is switched off, the emission of the light due to fluorescence ceases almost instantly.