Used in submarines, to ensure all interior lighting is red and of low intensity so as to preserve night vision. See "Darken Ship".

In submarines, to ensure all interior lighting is red and of low intensity so as to preserve night vision.

In the old days of submarining certain spaces in the boat would be rigged for red (all red lights) prior to going to periscope depth, when surfacing at night, or all the time in sonar. The red lights helped adjust eyes to the dark. Unfortunately, in later years studies found that the red light was actually irritable to the eyes and made people more aggressive. Other colors were tested and used, such as blue, yellow and eventually low level white (dirty gray)