Quantcast  Low Light Level

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(Sb2S3), a photoconductive surface, to form a pattern of different
electronic charges which is then scanned by a low-velocity beam of electrons
and converted to electronic signals.  The standard vidicon light sensitivity
range (spectral response) covers the bulk of the visible light spectrum and
approximates that of the human eye (see Table 9).  Supplemental lighting is
required for effective use below one foot-candle (dawn/twilight conditions).
A fixed scene may slowly "burn" itself onto a standard vidicon, and direct
viewing of a bright light, such as the sun, will cause the target to be
burned with subsequent image spotting.  The primary disadvantages of
standard vidicon cameras are the lighting requirements and their relatively
short life, but they are the least expensive and most widely used type of
camera.
6.2.1.2  Low Light Level.  Low light level cameras require less ambient
lighting than standard vidicon cameras and generally have a longer life (up
to one year).  The low light level camera is much more sensitive and
produces an effective image for alarm assessment down to light levels which
approximate full moonlight (0.01 foot-candles) (see Table 9).  Images will
not "burn" on these tubes, but their effective use in normal to bright light
requires the use of an automatic iris to prevent "blooming" (blinding) of
the camera.  Low light level cameras use a mosaic target of either a form of
silicon, cadmium and zinc teluride or other substance, which gives the
increased sensitivity, but otherwise operates like a standard vidicon.
Three types are generally available; Newvicon, Ultricon, and silicon diode.
Newvicon is a trademark of the Matsushita Electric Company, Inc.  Ultricon
is a trademark of the Radio Corporation of America.  Both are referred to by
their registered trademarks rather than their target materials.  They are
the cameras of choice when available illumination is in the visible
spectrum.  Ultracon tubes have demonstrated greater reliability in
Government agency testing.  Silicon diode are the cameras of choice when
available illumination is in the infrared spectrum.  Infrared illumination
often provides better visibility under some fog conditions than would
standard illumination.  The





 


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