A. Because the pupil (which contracted in the bright room) does not dilate instantaneously; and the contracted pupil is not able to collect rays enough (from the dark road or street) to enable us to see before us.
Q. Why do we see better, when we get used to the dark?
A. Because the pupil dilates again, and is able to gather together more rays; in consequence of which, we see more distinctly.
Q. If we look at the sun for a few moments, why do all other things appear dark?
A. Because the pupil of the eye (which was very much contracted by looking at the sun) is too small to collect sufficient rays from other objects, to enable us to distinguish their colours. (See “accidental colours.”)
Q. If we watch a bright fire for a few moments, why does the room seem dark?
A. Because the pupil of the eye (which was very much contracted by looking at the fire) is too small to collect sufficient rays from the objects around, to enable us to distinguish their colours.
Q. Why can we see the proper colour of every object again, after a few minutes?
A. Because the pupil dilates again, and accommodates itself to the light around.