I’m sure everyone knows what I’m talking about, but I’m genuinely curious as to what the process in our eyes and brain is, so that after a period of time we’re able to see relatively well even without much moonlight.
In: Biology
The pupil in your eye gets bigger so that it lets more light in. The muscles in your eye expand and contract to open up the hole. Cameras work the same way, if you open up the aperture more light will come in. Note that a negative side effect of having a large aperture (large pupil) means that light will be coming in from more angles which results in a less clear image.
Primarily it’s that your pupils (the black circle in the center of your eye) dilates (expands) to let in more light. In a bright sunny day your pupils are tiny pin-pricks, at night they get much much bigger.
Everyone here has mentioned pupils, and that’s *definitely* an important factor! However, there’s another part to the story.
Your eyes have two kinds of light-sensitive cells. One kind is called “cones”. The cone cells are good for seeing in color with good detail, but they need a lot of light to work. The other kind is called “rods”. The rods can’t distinguish between colors, but they’re good at working in low light levels.
Both kinds of cells work by containing chemicals that are sensitive to light–when light hits the cell, the chemical changes, and the cell detects that chemical change. The chemical in the rod cells is *very* sensitive. If you’re looking at a scene that’s *not* dark, there’s so much light that all that sensitive chemical gets used up. Your eyes make more, of course, but it gets used up as fast as they can make it so it never builds up to “normal” levels.
When you’re out in the dark, however, there’s a lot less light coming into your eyes, and the rod cells can “recharge” their supply of the sensitive chemical. After 20 to 30 minutes, your rod cells are fully recharged and your night vision is strong.
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