This blog article talks about cones and rods and visual purple and camping experiences from my childhood.
I imagine my first paying attention to rhodopsin and visual purple and rods and cones was many decades ago, when I would find myself having some camping experience as a child. So I read about all of this stuff, and of course I read about how in World War II the military aircraft would (during night time) use red-colored lighting in the cabin to try to minimize loss of night vision. The reason of course being that as compared with other colors of photons, red photons have less energy per photon. So the red photons are likely to cause less loss of night vision than photons of other colors.
And in those childhood camping days I learned the old astronomer’s trick. If you are trying to see something in the dark, something that is not very bright, the trick is to glance aside. Don’t use your central vision to try to see whatever it is, but use part of your retina that is off to the side from the central vision. The reason of course is that the central vision is mostly cones (color vision) and the areas away from the central vision have more rods (night vision). And it really works!
Lots of people will carry a flashlight when they are walking around at night, and will use the flashlight. What I found back in those boyhood camping days was that the dumbest thing I could do was to actually use the flashlight. The practical effect of using the flashlight was to lose my night vision, and then if I needed to see something important, likely as not I would need to turn off the flashlight and then allow my night vision to return, which would take at least a minute or two. And only then would I be able to make out whatever it was that I needed to be able to see in the dark.
So in those childhood camping days I got in the habit of carrying the flashlight but very consciously not using it. What I found was that if a person has the self-control not to use any artificial lighting, it is possible to find one’s way in the middle of the night just from starlight. No artificial lighting is needed and no moon is needed. The starlight by itself is enough to find one’s way, if one simply allows one’s eyes to adjust. Indeed it does not even need to be a clear night. Even if the night is overcast, the starlight comes through the clouds and it is enough for a person to find his or her way.
My primary care physician recently reminded me that this is part of why one’s daily multiple vitamin pills have vitamin A in them. The vitamin A is a precursor chemical for the rhodopsin that serves as part of the pathway in the rods for seeing in the dark.
So anyway what I find even now at my present age is that I am lucky about this. Even now the way it works for me is that I can let my eyes adjust to the dark and I can find my way by starlight.
Even now, the night lights that I use around the house are red colored rather than some other color. The idea is that the red-colored night lights will not cause as much loss of night vision around the house at night.
Did you already know the astronomer’s trick? If so, how did you learn it? Are your night lights red colored? Please post a comment below.