The best historical practice in one- to three-arm color light signals is shown here. Note that the lower arms only improve the aspect given by arms above them. Nevertheless, a light is shown in each arm at all times when the signal is to be observed, and the absence of a light was usually interpreted as the most restrictive aspect of the signal. Additional aspects were used by many companies, but the ones shown represent the majority of aspects actually used. Three-arm semaphore signals displayed the same aspects by night, and by day the arms assumed the corresponding positions.
The indications of the aspects are the same as for the PRR position-light signals except for the following two additional aspects:
Composed by J. B. Calvert
Last revised 9 May 1999