How come early morning light hurts my eyes?

Dilated pupils: Youi have been asleep and the pupils are dilated. When you awaken, large amounts of light enter the eye and the eye reacts to close down the size of the pupils. There may be spasm of the muscles doing this and thus pain. This is just like having your eyes dilated at the doctors office and going out in the bright light. It is a protective mechanism we have.

Sudden brightness: In the dark, your pupils dilate to allow in as much light as possible; the retina is also relying on its dim light receptors for all work. Your eyes are essentially primed to work in a dark environment. When exposed to sudden bright light, the pupils may take a second or two to constrict, allowing too much light, and the retina is "shocked" before adjusting to the sudden increase in light.