Red light helps watchstanders keep their dark-adapted vision
In darkness, the eye relies heavily on rod cells, which are sensitive to dim light but do not detect color well. They take time to become fully effective after exposure to bright light. A sudden burst of white illumination can therefore make it harder to see outside for a while—even after the lights go dark again.
Red light is useful because rods respond less strongly to long-wavelength red light than to brighter, shorter-wavelength light. A dim red-lit control space can leave a watchstander better prepared to look through an optical instrument into the darkness than a brightly lit room would. The advantage depends on keeping the illumination low: intense red light can also disrupt dark adaptation.
The lighting supports a change in what the crew needs to see
A submarine control room still has to be usable. Crew members may need to read instruments, consult charts, and monitor equipment, while someone on watch may need to shift attention to an optical view outside. Red illumination offers a compromise: enough light for nearby tasks, but less disruption to night vision than ordinary bright lighting.
That matters most when a submarine is operating where visual observation through a periscope or another optical device is relevant. The control room itself has no ordinary view through windows; the lighting is about preparing people’s eyes for the outside view when they use that equipment.
Red is a tool, not a guarantee of invisibility
The benefit is physiological, not magical: red lighting does not make a submarine harder to detect, and it cannot preserve night vision if the room is too bright. Its practical value is that it reduces the visual penalty of moving between close-up work and looking into a dark scene. A seemingly theatrical glow is, in effect, part of managing the crew’s limited ability to see in low light.
