Note 1 to entry: A light signal can be a reflected image of the light source, for example the use of heliographs.

Note 2 to entry: The term "light signal" is sometimes used for an object or apparatus that emits a light signal, but this usage is not recommended (see "signal light").

Note 3 to entry: This entry was numbered 845-11-02 in IEC 60050-845:1987.