Night Vision

Night Navigation: Red Light, Blue Tape and Black Eye Patches

Best Practice Versus 'Scientific Blunder.' Dimmable White Best, Says Coast Guard Expert

The following was published in an online subscription from Loose Cannon by Peter Swanson.

Ask an audience of cruisers to identify the optimal light for nighttime navigation, and most will answer that red is best. The question comes up from time to time in nautical Facebook discussions, and red is the answer endorsed overwhelmingly by commenters discussing how best to preserve “night vision.”

Night vision, otherwise known as “dark adaptation,” allows people to see better at night but this advantage can be lost in a flash when someone is exposed to bright light, even something as innocuous as opening the fridge door. It can take up to 40 minutes in darkness to regain one’s night vision. Conventional wisdom has long endorsed red light as a best practice to preserve it, hence the little red bulb in all those old compasses of ours.

Problem is: The answer is incorrect, always has been. “Rig for red,” as the Navy used to say, was never a best practice. It’s just that recreational boating followed the lead of the World War II military, which had actually misinterpreted the data. We’ve known this for over 20 years now thanks to the work of government scientists such as Dr. Anita Rothblum, a U.S. Coast Guard expert on maritime accidents, who called the red lighting initiative on World War II warships and submarines “a scientific blunder.” Rothblum and co-author Dan Wyatt wrote “Night Vision and Nighttime Lighting for Boaters” in 2002 and this is what they said:

In order to see a ship in the distance on a cloudy night, we need our rod vision. But in order to read charts and ARPA or (electronic charting) displays, we need our cone vision. And we can’t have both at the same time. Around World War II scientists were trying to figure out how to light Navy ships and submarines so that mariners could see well at night.

Someone noticed that the relative spectral sensitivity curve appeared to show that rods were almost insensitive to red/orange light, whereas cones were still fairly sensitive. Thus was born the concept of “rig for red.” The hypothesis was that if we used red lighting at night, we would be able to read charts and still protect our sensitivity in the dark.

Unfortunately, this is not the case. 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. Thus, it is impossible to read color-coded charts and displays accurately under red illumination.

In addition to causing eye fatigue, making it harder to focus, red lighting may also have a negative psychological effect, especially when a situation is stressful, according to Rothblum.

Dimmable White Rothblum’s paper, which was informed by mid-1980s research at the U.S. Naval Submarine Medical Research Laboratory, concluded that dimmed down white light was preferable at sea.

Major navies have gone to dimmable white lighting for night operations (and, depending on the circumstances, green or blue, too), and the rest of us should consider using dimmable white whenever practical.

“Recreational and commercial mariners should consider the advantages of using low-level white light on the bridge at night…When charts and displays need to be viewed, low-level white lighting greatly surpasses red lighting in supporting good color discrimination and, therefore, accurate reading of charts and displays.”

But that bring us to another issue, the proliferation of indicator lights—of all colors—confronting today’s watchstanders, particularly aboard powercraft.

Sailors have a standing complain against powerboaters, saying that they are too quick to shine their searchlights. To be sure, no one likes to have a powerful spotlight shined in one’s eyes while operating a boat. My personal theory is that overreliance on searchlights may happen because many powerboat skippers have aleady lost their own dark adaptation.

This is not a reflection on anyone’s competence. The reason that sailors better maintain their night vision has more to do with sailboat helm design. Normally sailors are working with a single darkened screen at the helm and a couple of gauges, so they are not faced with anywhere near the number of multiple small light sources found, say, on the bridge of a trawler.

Tape or Tech? Big stuff like a marine multifunction display can be turned down to nearly black, and PC navigational software can also be dimmed to black even if the laptop itself cannot. It’s all the peripheral illumination that gets you—instrument panel switches, inverter status displays, shifter and thruster lights, etc. And even if a screen is dimmable, say on the VHF radio, the process is unlikely to be intuitive. On a sailboat, most of these ancillary panels are down below, not in your face at the helm.

As one delivery veteran likes to say, running at night should be safer than during the day—there is less traffic and fewer distractions, and it’s more likely that the other boaters out there with you are the experienced types. But if you’re not eliminating those pinpricks of light at the helm, you might be the one too quick to reach for the searchlight.

Let this sink in: You’ve spent anywhere between $35,000 and $150,000 to populate your helm with modern electronics, but your 2025 universal dimming solution is analog—a $7.95 roll of blue painter’s tape to cover the multitude of sins.

Pirate Option Meanwhile, the woman who exposed the shortcomings of red light has a quaint suggestion, and one that might appeal to our inner Jack Sparrow.

“The two eyes adapt independently of each other,” Rothblum wrote. “To maintain the greatest degree of dark adaptation, one can place a black patch over one eye before turning on lights to read charts and displays.”

Rothblum explained the science behind this seemingly fanciful suggestion: “The patched eye will retain its level of dark adaptation (if little or no light leaks under the patch), while the unpatched eye can read the charts. When the lights are turned off again, take the eye patch off. The eye that was exposed to the light will need time to readjust to the dark. However, the eye that was patched will already be at or near its peak sensitivity.”

This just happens to be one of the theories behind portrayals of pirates wearing eye patches. Pirates may have worn eye patches just as Rothblum suggested: To preserve night vision as they moved from lighted to unlighted parts of their ships or engaged in night fighting.

Red night lighting is not going to kill you. You’ll be fine holding a course with red over your Ritchie. But please, Captain Sparrow, don’t insist it’s a best practice unless you think you know more about the subject than Dr. Rothblum, who co-wrote this: