It's because of light adaptation and dark adaptation of photoreceptors.When you are exposed to bright light,there will be more photobleaching of rods and cones.In a way senstivity of eye to light is reduced.When you are exposed to bright light for several minutes and suddenly if you see a dim scenary,you will see a sort of blurred,gray image.This is because it takes some time for bleached photochemicals to again return to normal form so that they can respond to light.