Why do we see black spots after turning our gaze from bright lights?



You look at the Sun or a bright light for a long time and then look away, at a wall, for instance. What do you see? Dark spots in front of your eyes. Sometimes, there are so many spots that you will not be able to see anything. This is because of photo bleaching or flash blindness (when the bright light in question is a flash). Such light changes will have an impact on the cells in the retina, which is the light sensitive part of your eye. There are two types of photoreceptor cells in the human retina, rods and cones. Rods and cones contain light-sensitive pigments, which react to different ranges of light frequency. When light strikes the retina, the pigments go through a chemical change, converting light into an electrical signal that is relayed to the brain via the optic nerve. The brain then translates the electrical signals into images a person sees.



When you look at a very bright light, the pigments get bleached or oversaturated. In other words, the pigments are used up and the cells have no more pigments to send signals to the brain. Hence you experience dark spots. The spots aren't exactly "black", they are just "no signal" areas. As the cells regenerate the pigments in the next few seconds, the sight returns to normal.



 



Picture Credit : Google


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