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 TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 9-1. Preheat fluorescent lamp and fixture components.
age may be another alternative for inaccessible lo-
a. Mercury lamps. The maintained light output of
cations. By operating the lamp below its rated volt-
mercury lamps is high because the electrodes oper-
age, the life is increased but the light output is
ate at a relatively cool temperature resulting in less
sacrificed.
oxide contamination of the operating electrodes and
the discharge gas. Long average life (24,000 hours or
9-4. High intensity discharge lighting (HID).
more) is a primary characteristic of most mercury
High intensity discharge lamps are those which
lamps. While some models may have lamp bases the
have a gaseous discharge arc tube operating at
same size as incandescent lamps, standard mercury
pressures and current densities sufficient to gener-
lamps must never be used to replace a burned out
ate desired quantities of visible radiation within
incandescent lamp (fig 9-2). However, there are self-
their arcs alone. Every HID light source-mercury,
ballasted mercury lamps which can be used as direct
metal halide, or high or low pressure sodium re-
replacements for incandescent lamps. The installer
quires a ballast. Without a ballast, the lamp will not
should check which type is compatible with the fix-
work; the arc will act as a short circuit and the lamp
ture before turning on the power. An objectionable
will destroy itself. Not only is a ballast necessary for
characteristic of mercury lamps is the time required
lamp operation, but a properly matched ballast is
to reignite (several minutes) after a momentary loss
essential to achieve rated life and performance with
of power. It should be noted that this lamp can cause
any HID lamp. Therefore, all ballasts should be
serious skin burn or eye inflammation from ultravio-
designed to match the supply voltage with lamp
let radiation if the outer envelope of the lamp is
requirements, to start the lamp and to control its
broken or punctured, and the arc tube continues to
performance throughout its life according to data
operate. Lamps allowed to operate in this way con-
published by the lamp manufacturer. Ballast de-
stitute both a fire and a personnel safety hazard and
signs differ widely between mercury, metal halide,
should be replaced promptly. There are certain
HPS and LPS light sources and are therefore not
lamps available that will automatically extinguish
interchangeable.
when the outer envelope is broken.
9-2
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