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arc in a Metalarc lamp and all other electric discharge
lamps operated on a 60-hertz alternating current is
completely extinguished 120 times per second. The light
output of the lamp is modulated at this rate. This variation
is greater in a clear lamp than in a Metalarc/C or a 3K
Metalarc lamp. With the phosphor-coated lamps there is some
phosphorescence or "carry-over" action. That is, the coating
continues to glow for a short period of time after the
radiation from the arc is cut off. However, there is still a
rapid variation in light output, which, under certain
circumstances may produce what is called stroboscopic
effect. Because of the stroboscopic effect, an object that
is moving at a uniform speed may appear to move in jerks.
Under the most extreme conditions, a rotating object, such
as a flywheel, may seem to be standing still or even
rotating in a reverse direction. Stroboscopic effect is
often unnoticed, and in most installations it is not a
problem. It may be reduced by operating pairs of lamps on
lead-lag type ballasts or groups of three lamps on separate
phases of a three-phase circuit. Many installations of
Metalarc lamps are performing satisfactorily in areas where
very fast motion occurs, such as machine shops, gymnasiums,
tennis courts and other sports areas.
The
physical, electrical and photometric characteristics of
Metalarc lamps are given in Product Information and
Specifying Guide MA-143R2.
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