Why does bright light help one to see details?

I wonder if it’s because it causes the pupil to dilate allowing more light in and more of the object one is looking at.

I think we’ll need someone who knows more about eyes to get a definitive answer.

Two things. I think #2 matters more for close-up work.

1)
Bright light makes the pupil contract, not dilate.

A smaller diameter aperture in a lens (like the eye) gives more depth of field – meaning things more things are in focus, whether they are near or far.

Dilation (a larger aperture) would cause short depth of field – things at one distance are focused, things nearer and farther are fuzzy.

Here’s an illustration of short vs vs long depth of field.

2)
Image sharpness depends on contrast, and bright light gives more contrast.

Think of black text on white paper. To the eye, the black ink does not vary much between dim and bright light – it’s very dark. But the white paper can go from very dim to extremely bright as you turn up the light level. The contrast increases and you can read the text better.

Like a camera lens, the brighter light narrows your pupils and your depth of field increases. The precise range of the object is now seen in greater (sharper) detail.

the brighter light narrows your pupils and your depth of field

Backwards. “A smaller diameter aperture in a lens (like the eye) gives more depth of field”

Bright light sharpens the color of the objects. When the color is sharpened, eyes pick up the details of the object better. That is why they use sewing lamps. When the light shines on the needle, the eyes are able to clearly see the thread hole (sharpened image). When you walk into a dark room, all you see is hazy silhouettes of items. In a few seconds the eye adjusts itself and picks up whatever light it can and that is when we start seeing definite shapes and start identifying the objects. Switching on the light in the room will instantly define the room perfectly for us…it is the same principle with sewing lamps.
Also, as people get older, the eye’s ability to pick up random light on its own diminishes. For example, in a restaurant, you can see some people easily reading the fine print on the menu, in dim light. Some can’t do that….they pick up the menu, bring it closer or move it towards a light source to get a better view….they do that because their eyes can’t pick up random light on its own and needs the aid of external light for better vision. Sewing lamps serve that purpose too.

@Jay Thanks for the correction. :)

The cone cells in the eye are packed closely together in the fovea, giving much higher resolution. Cones are activated by brighter light.

@Call_Me_Jay When you quoted me, you left a word out.

@kritiper I sure did. I’m the one who got it backwards. Sorry about that.