Lake Martin Boaters
member Chris Ray offered this detailed explanation on why using docking lights as headlights is dangerous;
“When you’re in the dark, your eyes adjust to allow you to see with less light. Sit outside for a while in the dark, and you’ll start to notice that you can see more by moonlight and even starlight without using an artificial light source. If you’re boating at night, you want your night vision to be as adapted as possible to see obstructions and other craft on the water. This adjustment to the dark takes some time, about 30 minutes for the full effect.
However, if you look at a white light source, your eyes immediately adjust for the brightness, and you lose your night vision. A quick flash here or there or a dim source won’t diminish it too much, but the longer you look at a white light source, the longer it takes for your night vision to recover. A single boat coming toward you with bright docking lights on can diminish your night vision for several minutes so that you can’t see obstacles.
Most people who have driven or ridden in cars all their lives instinctively think headlights are a good thing that light up the way in front of them. What you don’t notice is that your night vision is diminished, and although you can see the road, you can’t see as well into the areas on each side. Lighting up what’s in front of you will cause a higher contrast so that everything else appears darker. That works okay with a car because you usually only need to see where you’re going, which is clearly marked with lines for you (and others) to stay inside.
With a boat or aircraft, however, you not only need to see in front of you, but also to the sides. If you can’t see what’s to the side, you can’t turn the boat without risking impact with an unseen obstacle. If another boat is running dark, night blindness will prevent you from seeing it approach from the side and risk a collision. You generally don’t need to see cars coming at you with no lights from off road.
If you leave the lights off, however, you actually see more all around you once your night vision has adjusted. And you really don’t lose that much vision in front of you, because the water’s surface doesn’t reflect the light back at you the way a road does. Docking lights do so little on open water that sometimes people may not even realize they’re still on.
To reiterate, this is all about *night* vision. There’s no reason to get upset about people who have their docking lights on when there’s still daylight. They’re not hurting anybody until the sun goes down.
And one other note: Whereas white light diminishes night vision, red light doesn’t, at least not to the same degree. That’s why pilots use red flashlights in their cockpits at night, and why tail lights and brake lights on cars are red. Keep that in mind if you use a flashlight on your boat. You can night blind yourself with a white flashlight, but putting a red lens on it will reduce your recovery time considerably. A lot of nice flashlights (like Maglites) have lens kits readily available for this reason.”