Black spot when switching intensity of light Whenever I look at a bright light source and then turn my eyes away I see a large black dot blocking a part of my vision. Does this has something to do with Physics as it involves light or it is related to neurology.
 A: It is called photo bleaching. 
It happens to the cells in your retina. Basically you overload them with too high intensity of light (too many photons).
It is called overstimulation. It is because your retina is less active when light shines on it normally, and more active in darkness.
But the retina needs some time to adjust, and when you look into intense light too suddenly, it cannot cope with it, and your retina does not have time to deactivate itself, and the cones will overload (get overexcited).
This is a process called photo bleaching. After this, the cones and the retina will need some time to re-adjust to less light again (activate itself to normal conditions).

In optics, photobleaching (sometimes termed fading) is the photochemical alteration of a dye or a fluorophore molecule such that it permanently is unable to fluoresce. This is caused by cleaving of covalent bonds or non-specific reactions between the fluorophore and surrounding molecules.

(From Photobleaching in Wikipedia.)
A: The black spot you refer to is a biological phenomenon which is only related to physics in the sense that all biological processes have to obey the laws of physics. In the retina of the human eye there are cells called rods and cones which have a light sensitive protein called rhodopsin in their outer membranes. Rhodopsin breaks down when exposed to light, and this change triggers electrical nerve impulses to the brain. The rhodopsin is later repaired and ready for re-use. Staring at bright lights uses up a lot of rhodopsin, so when you look away there is a black area of rhodopsin deficiency which takes a while for the retina to restore.
