Erm..-achromatic-ocular-functionality-lmao?!

Erm..-achromatic-ocular-f...

I was wondering why (when I'm in the dark);
It's harder to focus directly on a light source(like a window), but the light source is earier to distinguish through peripheral vision(looking at something else.)

Also, in a dark room, if you turn attention to the light beneath the door, wherever you focus it seems to be darker, like a shadow(except it's not.)

I was just curious. >3

It has to do with rod cells and cone cells and their relative effectiveness of seeing in varying light conditions.
Here's a couple links from wikipedia:
http://en.wikipedia.org/wiki/averted_vis...
http://en.wikipedia.org/wiki/scotopic_vi...

The Myth Busters also did an interesting episode on the pirate eye patch. They explored the idea that it is advantageous to cover one eye in the sunlight so that if you go below decks where its darker and uncover that eye, it would be acclimated to the light level and you could move about immediately without having to wait for your recently sun-drenched eye to get used to it.