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A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, to produce ultraviolet and make a phosphor coating in the lamp glow.
New lighting systems have not used magnetic ballasts since the turn of the century, however some older installations still remain. Fluorescent lamps with magnetic ballasts flicker at a normally unnoticeable frequency of 100 or 120 Hz (twice of the utility frequency; the lamp is lit on both the positive and negative half-wave of a cycle).
Cross section of a typical fluorescent lamp with and without a reflector. Some lamps have an internal opaque reflector. Coverage of the reflector ranges from 120° to 310° of the lamp's circumference. Reflector lamps are used when light is only desired to be emitted in a single direction, or when an application requires the maximum amount of ...
Light fixtures currently in use usually provide students and teachers with satisfactory visual performance, i.e., the ability to read a book, have lunch, or play basketball in a gymnasium. However, classroom lighting may also affect students' circadian systems, which may in turn affect test scores, attendance and behavior. [1]
They give light immediately on startup, but usually need a few minutes to restrike if power has been interrupted. Because of the light emitted by the filament, they have slightly better color rendering properties than mercury-vapor lamps. Self-ballasted lamps are typically more expensive than a standard mercury-vapor lamp.
A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for incandescent bulbs.