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Color Light Signals


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. 


Mounting Systems

Lenses and Aspects

More Details

Above.  Internal view of lower signal housing showing
terminal block and common dropping resistor used for all
three lights.