There's a lot of discussion about size of human eye pupil during twilight and night conditions and appropriate bins for such conditions. It is generally stated that during moderately cloudy day:) the pupil is about 3-4 mm big, and during night it reaches 6-9 mm. Please feel free to correct me if I'm wrong.
But what is the size of one's eye pupil during a sunny day and very sunny bright day in the middle of the summer(lets say north mediterranean climate)? I've never measured size of mine but I suppose it may be as small as 1.5-2 milimeters. Am I right?
I think it may be useful to provide such information in one thread, and if not maybe at least my curiosity will be satisfied
The usual numbers are
2mm on a bright day
3mm in overcast
4mm at very dim twilight (owling ... end of birding)
5mm in urban/suburban dark
7mm at a good dark site
But the variation over the population is about plus or minus 1mm even more at the large sizes in older people.
A lot of people seem to overestimate the sizes.
You can measure your own (and get rid of all the variation) with a digital camera with a flash (no red eye that's what you want to measure!) and a ruler. Hold the ruler on your forehead for scale and self-shot in the light environment you want to check.
I'll post a chart later.
There is also a way to measure the size of your pupils with a binocular in front of your eyes. You need a glitter point on a sunny day (tiny reflection of the sun in a small round shiny object). Focus the binocular at infinity and look at the glitter point at some close distance like 5m. You will see a large unfocused disc. That is actually an image of your eye's pupil (or the exit pupil of the binocular if your eye's pupil is larger than the exit pupil). I'll leave it to your ingenuity to fashion some sort of adjustable paper caliper to place in front of the binocular objective. Adjust the caliper until you see both inside edges of it just barely impinging on the projected disk of your pupil in the binocular. Divide that measurement by the magnification of the binocular and the result is the size of you pupil under that particular lighting condition with a binocular in front of your eyes. This can also be done in low light with a pinhole in aluminum foil covering the lens of a flashlight.
It's surprising to me how large my pupils open when looking through a binocular in a heavily shaded area in daylight, around 5mm. In very bright sunlight my pupils constrict to barely more than 2mm when looking through binoculars.