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Fluorescence is the emission or glowing of visible light by a substance that has absorbed light or
other electromagnetic radiation. It is a form of luminescence which means light is emitted without
heat. In most cases, the emitted light has a longer wavelength, and therefore lower energy than the
absorbed radiation.
The most striking examples of fluorescence occur when the absorbed radiation is in the ultraviolet
region of the spectrum, and thus invisible to the human eye and the emitted light is in the visible
Fluorescence has many practical applications, including mineralogy, gemology, chemical sensors
(fluorescence spectroscopy), fluorescent labelling, dyes, biological detectors, and, most commonly,
fluorescent lamps.
A fluorsecent lamp consists of mercury vapour contained at a low pressure in a glass tube with a
fluorescent coating on the inner surface, putting a current through the tube causes
ionisation/excitation due to the mercury atoms and electrons colliding emitting ultraviolet visible
photons. The ultraviolet photons are then absorbed by and excite the fluorescent coating, when this
coating de-excites it emits visible photons, causing the tube to fluoresce/glow.
The structure of an atom dictates the kind of photon produced, and therefore the wavelength or
colour of light. Although fluorescent lights are much more efficient than light bulbs and last much
longer, people generally prefer incandescent light bulbs in the home, as the light is closer to the red
wavelength. This makes it appear "warmer." The bright glow of fluorescent lights is shifted towards
the "cooler" blue spectrum. Fluorescent lights are used extensively in commercial buildings, parking
lots, garages and parks.
David Shaw


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