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 |
