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quote:Originally posted by chrisBut during the daytime it is too bright for the sensitive rods so they are masked by a layer of melanin (the substance responsible for a suntan) at the back of the eyeball.When it gets dark suddenly (if you go into a dark place from somewhere well lit) the reason that your eyes take a while to adjust is partly down to the delay in unmasking the rods from their protective pigment layer.Chris"I never forget a face, but in your case I'll make an exception" - Groucho Marx
quote:Originally posted by RokitanskyThis is a classical physiology question. Generaly, there are three ways of the adaptation on darkness.1st Neural adaptation is the fastest, It includes neurons in the optical pathway and in the brain. It`s not very great, it allows the eye to adapt to 2-3X lower degree of lightness.2nd Changing the diametar ot the eye pupil accounts for up to 30X change in the degree of adaptaton. It`s also fast.3rd In the dark, quantity of photosensitve pigment in rods and cons is increasing in the absance of light. This can take several minuts for full adaptation, but the degree of it is very high, up to 25 000 X. Cons are being adapted faster then rods, but they adapt to a far less extent then cons.All three types of adaptation are performed simultaniously.