light  

I'm thinking it has something to do with the fact that your pupils change sizes in different lights. In a dark place, say a movie theater, your pupils enlarge to take in more light so that you can see better. But, in a bright place, say outdoors during the daytime, your pupils get small keeping too much light from entering your eye preventing you from being blinded. When you move from one to the other your pupils need time to adjust to the new lighting.

i do experienced that too seeing nothing when im going to enter a theater ..maybe its a matter of adaptation in our eyes...coz the darkness turns into somewhat lighter if weve been their long just like 5 mins. or so..

It takes time for the eyes to adjust.
I am always amazed at those type of glasses that
adjust colour to the different lights immediately.
I wear such glasses.

our eyes needs to adapt first to the new environment ..in my experiences ..i just close my eyes first before opening it as to make it more acquainted with the dark