Why Submarines Switch to Red Lighting at Night

When a submarine needs to come up to periscope depth, every second exposed near the surface is a second it can be spotted. So before the scope breaks the waves, the crew running it has typically spent time working under a specific kind of lighting: dim red, not the bright white or fluorescent glow used elsewhere on the boat.

The standard explanation, repeated across defense outlets and submarine tradition alike, comes down to a chemical called rhodopsin. After roughly 20 minutes in low light, the human eye starts producing it, and rhodopsin is what activates night vision. Bright white light causes rhodopsin to break down almost instantly, forcing the eye to start the 20-minute process over. Red light, because of its long wavelength, doesn't trigger that breakdown, so a crew member working under red light keeps night vision intact and ready the moment a scope needs to search real darkness on the surface.

The Physics Van, a science outreach program run by the University of Illinois physics department, puts the submarine case alongside a few familiar cousins: "some submarines use red interior lights for the same reason as airport control towers (at night), planetariums, and some movie theaters. The reason is that it's easier for your eyes to adjust from red light to dark than from white light to dark." Submarine crews get a second benefit layered on top: red light barely touches melatonin production, so sailors running an overnight watch schedule can still get real sleep under the same lighting that keeps them alert for a periscope shift.

The rig-for-red tradition dates to World War II

The name for this practice, "rig for red," is old — old enough that its scientific basis was set by wartime researchers working from an early and incomplete picture of human vision. That's where the story gets more complicated than the standard explanation lets on.

Dr. Anita Rothblum, a U.S. Coast Guard human-factors researcher, examined the practice in a 2002 paper and reached a blunt conclusion, reported by boating publication Passagemaker: rig for red is "a scientific blunder." Her argument isn't that red light fails to protect night vision — it does that part fine. It's that red lighting quietly breaks something else: the ability to read anything color-coded. "Red text on a white background — easily readable under white light — may appear uniformly red (and therefore unreadable) under red light, because they both reflect red light equally well," Rothblum wrote, adding that the practice can also cause eye fatigue and subtle psychological strain in an already stressful setting.

Rothblum's paper drew on research from the Naval Submarine Medical Research Laboratory in the 1980s, which had already concluded dim white lighting served sailors better than red at sea. It hasn't fully displaced red bulbs, on submarines or on the recreational boats Rothblum was originally writing about; old habits, and old red bulbs already screwed into fixtures, are hard to dislodge. But the clean version of the submarine red-light story, pure science with no downside, leaves out the part where the Coast Guard's own researchers spent a career arguing the tradeoff is worse than sailors assume.

Museums that preserve retired submarines still teach the red-light tradition as a matter of course. The Independence Seaport Museum in Philadelphia, home to the decommissioned USS Becuna, walks visitors through exactly why the boat's control room could swap its white bulbs for red ones during a real patrol. It's a piece of Cold War-era submarine culture that outlived the specific hardware it was designed for, even as the science underneath kept moving.

None of that changes the core physics: red genuinely is gentler on rod vision than white. It's the idea that there's no cost to using it that hasn't held up, a pattern that shows up elsewhere in how popular science explanations outrun the research behind them. A submarine's control room, like a lot of technical spaces built around mid-century assumptions, is still catching up to what vision science learned decades later.