Why when someone moves from light to dark place he experiences a "momentary blind" condition?
Because of management of ratina
When we are outside the light is much more than our eyes needs so our ratina becomes small to protect our eye from damage. If ratina does not manage its size extreme amount of light passes through our eyes and this extreme amount of light harms our eyes. But when we go to dark room, the amount of light is small so big size of ratina is needed but ratina takes a small time to change its size. That's why for that duration we experience blindliness.