Without getting too out of hand, it has to do with combining/splitting and recombining
chemicals retnal and opsin, and their product chemical rhodopsin. Rod cells, which
in effect are your night vision, are sensitive to rhodopsin. When a photon interacts
with rohodopsin, it splits it into it's component parts, retnal and opsin. And the
rod cell interperts that chemical reaction as light. retnal and opsin recombine at
a fixed rate. The "strength" of the ohodopsin has a lot to do with how much retnal
is available, and retnal is a product of Vitamin A (retinol), is derived from beta-carotene
blah blah blah.
It's commonly held that smokers hold less serum retinol (and therefore retnal) than
non-smokers. In fact, by a good amount. The common sense conclusion is that smoking
impacts the retnal uptake of beta-carotene. Makes sense. The good news should be
though, that drinkers show more serum retinol than non-drinkers.
So, drink up!
Anyway, the real clue here is that if you want better night vision, eat more carrots.
Vitamin A really is key to night vision. That and training your eyes for the dark.