Color Light Signals
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Color light
signals are the most common railroad signal in use today.� Their simplicity of design and low
maintenance costs makes them real winners. Each module of a color
light signal has a two lens design consisting of an inner doublet lens and an
outer doublet lens.� The inner doublet
lens contains the aspect color and has concentric prisms.� It is 5 1/2 inches in diameter.� The outer doublet lens is clear and also has
concentric prisms.� Most outer doublet
lenses also have an integral center deflecting bullseye or close-up prism to
allow viewing the indication when closer to the signal.� The outer doublet lenses are 8 3/8 inches
in diameter.� Unlike traffic lights and
grade crossing signals, color light signals do not have a reflector behind
the light source.� This is to avoid
phantom signals being created by railroad headlights. Original color
light signals were made from cast iron.�
Later signals, like the one shown on this page, were made from cast
aluminum.� Today, color light signals
are also made from polycarbonates in addition to aluminum. Modern color
light signals often include �rear-serviceable optical modules� which include
both inner and outer doublet lenses, as well as the lamp and socket, all in
one unit.� These units can be removed
from the rear of the signal for inspection, cleaning or replacement without
going around to the front of the signal.�
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Above.� Internal view of lower
signal housing showing |
