Why do you still "see" a bright spot when you close your eyes after you have looked directly into the Sun or any other light source?
This is called a positive afterimage [2]. The cells in your retina are full of light-sensitive pigments, and when you look at a bright light, like the sun, these pigments get excited and send electrical impulses to your brain [1, 2]. The exact mechanisms behind positive afterimages are not well understood, but researchers believe that the phenomenon might be related to retinal inertia [2]. The original image stimulates nerve impulses, and these impulses continue for a small window of time after you close your eyes or look away from the scene [2]. It takes the cells in your retina some time to respond to light, and once the cells have been excited it takes some time for that response to cease [2].
When you look at an object, the photoreceptors in your retina translate light into vision. [1] If you look at a very bright light source, such as the Sun, for a long time, or if you look at a bright light bulb, your photoreceptors can become overexcited. [1, 2] This means that when you look at a normal level of light, you may still "see" a bright spot. [1] This is because the photoreceptors in that area of your retina have been photo-bleached, and it takes a while for the pigment to regenerate. [1, 2] During this period of time, you may continue to see the bright spot because the photoreceptors in that area are not active when light shines on them. [2]