April 5, 2016

Seeing things at night

WHEN YOU’RE OUT AT SEA, far from the bright lights of civilization, it’s amazing how much you can see at night. The sensitivity of the human eye is much greater than most of us give it credit for. It takes a little time, 20 or 30 minutes, to develop full night vision, and it’s an asset little understood and little appreciated by people whose town lives are brightly lit wherever they find themselves at night.

Night vision is, in fact, a wonderful gift from Nature, a manyfold heightening of visual acuity that vastly increases a person’s ability to see in the dark. On the other hand, your night vision will be destroyed in a flash if you glance at a bright white light.

That’s why compass lights are red, not white. Red light has almost no effect on night vision, so if you have to go from the deck down to a brightly lit cabin at night for a brief period, you should try to protect your night vision for when you return topsides. There are a couple of ways to do this, neither terribly suave and debonair, but worth the effort. The first is to wear red ski goggles while down below. The second is to close one eye until you get back on deck. Half your night vision is better than none, and in 20 minutes it will be fully restored.

While we’re talking about lights, it’s interesting to note that at night a fixed or flashing point of light appears to jump around the horizon. Sailors know this phenomenon well and psychologists call it autokinetic illusion. And illusion it is. It comes about through imperceptible eye movements or strain of the eye muscles when we stare fixedly at one point for too long.

The light always reappears some distance to the right or left of where we expect it.

Now here’s a suggestion for finding a faint light, such as a star, at night: Look a little to one side, or above or below, of where you expect to see it. The reason for this is that if you look straight at an object, the light rays focused by your eye fall on an area that is not as sensitive as the surrounding areas, so faint lights are often first seen in or toward the “corner” of your eye.

Finally, never try to judge your distance from a single light at sea at night. A single point of light provides no clues by which our perceptions can judge its size and distance with any accuracy. Changes of size and gradual increases in brightness as you approach remain imperceptible to the human eye. In many cases when the light is visibly nearer, you are in danger of running into it.

Today’s Thought
Vision is the art of seeing things invisible.
— Swift, Thoughts on Various Subjects

“And how would you like your hair cut, sir?”
“Yes, sir, but what style?”
“What are your prices?”
“Haircut $15, shave $10.”
“So, okay, shave it to a short back and sides.”

(Drop by every Monday, Wednesday, Friday for another Mainly about Boats column.)

No comments: