Why do submarines go red at night?

Why did submarines start using red light?

In the Second World War, submarines stayed submerged by day and surfaced at night to recharge their batteries. The lookout had to see straight away. An eye coming from a brightly lit control room needs time to adjust to the dark, and nobody wanted to lose that time on the surface. The answer was red lighting inside the boat. A review from the US Navy's submarine medical research laboratory in Groton puts it plainly: red lighting was instituted during the Second World War so crews could stay dark-adapted.

As early as 1946, the Navy's medical research department in New London measured how the red light in the conning tower affected night vision. It concluded that the red lighting of the time was adequate and did not seriously interfere with dark adaptation. The routine got a name that lives on in submarine films: rig for red.

Did the red light really protect night vision?

Yes, but less than people assumed. In 1984, S. M. Luria and David Kobus at the same laboratory reviewed the research. After very bright light, an older study found it took about 15 minutes longer to dark-adapt after white light than after red. After dim light, the gap shrank to around two minutes. On board, the light was dim. At the levels measured under rig for red, switching to equally dim white light would add about one and a half minutes to full dark adaptation, according to the report.

Two years later it was tested at sea. Three watch sections each stood one six-hour watch under dim white light and one under dim red. The crews preferred white, and the 1986 report from the Naval Health Research Center recommended dim white as the standard for night lighting. The Navy's own researchers questioned the red light 40 years ago. What lighting today's submarines use, navies do not publish openly.

What does red light have to do with the body clock?

Night vision and the internal clock are two different systems. The clock is set by cells in the eye that respond most to blue light. George Brainard and colleagues shone single wavelengths between 420 and 600 nm on 72 volunteers and found 446 to 477 nm suppressed melatonin most (Journal of Neuroscience 2001). Red light sits far from that band. We explain how the cell works in The eye's third cell type.

So the red light on submarines happened to have a property that later caught sleep researchers' attention. But it was chosen for the periscope, not the bunk.

How does the Navy think about light and sleep today?

The focus has moved from seeing to sleeping. A submerged submarine has no sunrise and no sunset, and the crew stands watch around the clock. Within the last decade, the US submarine force moved from an 18-hour watch day, six hours on and twelve off, to a 24-hour day with eight hours on and 16 off, according to USNI News in 2021.

Then came the light. In 2015, researchers at the Lighting Research Center fitted fluorescent lamps rich in blue light, 13500 K instead of the standard 4100 K, on a US submarine running a 24-hour schedule. They reported that the crew's activity rhythm and melatonin lined up better with the schedule (Journal of Biological Rhythms 2015). Then came the glasses.

What did the Navy's glasses study find?

The study ran on a Virginia-class submarine out of Groton and was published by the laboratory in 2022. 42 submariners were randomised into two groups. 23 got glasses that emitted blue light peaking at 470 nm for about 40 minutes after waking, and orange safety glasses that attenuated 400 to 510 nm for about two hours before sleep. 19 wore only an activity tracker. The trial lasted 12 to 14 days.

The glasses group slept 431 minutes a night on average, the control group 405. The difference was a trend, not statistically significant (p = 0.06). Melatonin could not be analysed because only 10 of 84 saliva samples gave usable values. The sailors wore the orange glasses for 80 minutes per session on average, and 5 of 23 said they sometimes got in the way of their duties. The researchers call the results preliminary.

Is it true that submarines go red after dark?

Historically, yes. Submarines used red light at night from the Second World War onwards. But the reason was night vision, and the Navy's own reports from 1984 and 1986 proposed dim white light instead. When the Navy later turned to sleep and body clocks, what it tested was orange glasses before sleep and blue light in the morning, not red control rooms.

What does it mean for an evening at home?

The logic is the same as on the submarine and on the space station: plenty of light by day, little and warm light in the last hours. NASA did the same with the lamps on the ISS, which we cover in Why did NASA change the light on the space station?. At home you cannot change every lamp and screen, but a lens changes all the light that reaches the eye at once.

Red · Night in LOWLIGHT 05 filters 99 % of light between 400–550 nm. Orange · Evening filters 98 % of blue light. The figures come from the supplier's lens data and describe the lens, not your sleep. The red lens is for the last hours on the sofa, at the screen or with a book in bed. Never in the car or outdoors in the dark, where you need to see everything.