How long do your eyes need to adapt to darkness and reach full contrast?

Question

I heard you should wait some time until your eyes adapt to darkness and are able to see smallest luminosity differences, otherwise you might overlook faint objects in the ocular. Are there any rules of thumb here?What about looking for 5 minutes on your bright laptop, do you have to wait again the same time or wear some sunglasses? ;)

Answer 1

It takes about 20 minutes for the night-vision cells - the rods - to take over for the day-vision cells - the cones - in the retina. If you use the cones again for 5 minutes, the already-active rods will kick right in.

Also remember that rods have no color perception:

"Cold-hearted orb that rules the night,

Removes the colors from our sight,

Red is grey and yellow white,

But we decide which is right,

And which is an illusion."

-The Moody Blues, 70's prog rock band.