What happens to your eyes if you are in the dark for a long period of time and then exposed to light?

Nothing dangerous: Eyes adapt to both light and dark fairly easily. In the dark, the pupils dilate to allow in whatever light there might be, and the retina's dark-seeing receptors (rods) are capturing the images you see. Once you enter the light, the pupils constrict rapidly and forcefully which may cause temporary discomfort. You may also find things excessively bright, but there is no danger in healthy eyes.

Dark adaptation: The pupils will constrict when going from dark to light to decreased the light coming in.This is immediate.Retinal adaptation is slower.You may notice that when you go into a dark room your ability to see slowly increases.This is retinal adaptation.Conversly when going from dark to light things will seem too bright until the retina adapts.Typically your eyes will not be harmed by normal light.