You might have noticed that after the bright light from a camera flash goes off, you start seeing bright spots followed by a temporary loss of vision. This is usually more observable if you were in a dark room before the flash went off or when you stare directly at the sun. This is referred to as flash blindness.
Flash blindness happens when the light sensitive retinal cells (located at the back of your eyes) get over-stimulated or bleached by a more intense light than what the cells are adapted to at that particular moment. The retinal cells are unable to convert all the light rays to electrical impulses that the brain can interpret. This causes a momentary disruption of vision. There is usually no long-term effects if the light source is the flash from a camera.