The Lake County Astronomical Society

Better Night Vision

Jack Kramer

At an observing session, we all use red-lensed flashlights for illumination; this is to preserve our night vision. The ability of our eyes to become dark-adapted varies to some extent for each individual, but the rule of thumb seems to be that it takes about a half hour to become dark-adapted. Since our eyes don't perceive red light as strongly as other colors, it doesn't affect our low light sensitivity as much as do the other colors. But in addition to using a red flashlight, here are a few more tricks.

One technique to speed up dark adaptation was suggested by Vic Stryker, who was a planetarium director in Arizona. This suggestion was originally published in the AAVSO Journal. Says Vic...

While standing up, look down at your feet and blink your eyes as hard and as rapidly as you can for a count of fifteen seconds. If there is no stray white-light contamination about, you will become totally dark- adapted in this time...Note this technique works for approximately 40% to 60% of those who try it, and in some cases the level of dark-adaptation can improve with practice. A word of caution to contact lens wearers: be careful not to dislodge your lenses...

A red flashlight still has an adverse affect on our night vision...just to a lesser extent than white light. The problem becomes especially acute when you're searching for some faint object and are constantly going back and forth between your eyepiece and the charts. Each time you return to the telescope, you'll often note a loss of acuity for a short time. Since I use my right eye to peer into the eyepiece, I've gotten into the habit of closing my right eye while looking at charts or notes, then opening it again after I've turned off the flashlight. This works very well.

Many observers report improved visual acuity if they leave both eyes open. We tend to squint with the unused eye while looking through an eyepiece; as I understand it, this tenses the eye muscles and adversely affects the eye that you're using. To make this easier, some use eye patches to cover the unused eye. I can't say that I note an improvement in acuity, but it is more relaxing to keep both eyes open. If you use an eye patch, get one with a convex surface; your eyelids may rub annoyingly on a flat eye patch.

I've noted that a number of observers (especially out West) wear sunglasses during the day and into twilight; I don't think they're doing that just to be cool. We've all heard about the dangers of ultraviolet radiation from the Sun and its effect on our vision. When you come indoors on a sunny day, there's a noticeable loss of sensitivity - the room looks so dark! It seems logical that the effects of lengthy exposure to very bright light would linger perhaps longer than the normal dark adaptation period. Regular use of sunglasses should help.

Under the heading of dark-adaptation is the simple expedient of installing a cutoff switch for the dome lights in your car or van. This way, if you have to get something from your vehicle, the dome light won't come on and flood your eye with all that nasty white light...not to mention bothering other observers. (Astrophotographers tend to become especially testy about this.) I've been meaning to put in a cutoff for years and finally got around to it recently. It's easy to install a toggle switch in the wire off the fuse panel under the dashboard (though you may have to be a contortionist to get at it).

If you have any other suggestions for improving night vision, let's hear about 'em. For example, has anyone tried those red observer's goggles or something similar?