Why do i see flash of yellowish lights in the corner of one eye after i turn out the lights?

Retinal Irritation: Light flashes indicate that the tissue that you see with, called the retina, is being irritated. The most common cause is rapid cessation of eye movement, which can cause your eye muscles to stretch the wall of your eye. Or, sudden normal movement of the gel inside your eye, usually after the age of 60, can stretch the retina. Dark spots in your vision mean that you need to see an eye doctor.