I have used two knots and 65 feet of 3/8nylon rope for years to lower myself to the ground,the bowline on a bight to make a saddle to sit in and the tautline hitch (safety belt hitch) to slow my decent. I have almost never climbed down in the dark. Always feel safe and never have to worry how will I get back to the ground should something go wrong.

http://www.animatedknots.com/bowlinebight/index.php

This second link scroll down and look to the right at the safety belt hitch that is what I use.

http://www.animatedknots.com/rollinghitchclimbing/index.php

I will be glad to explain moreif anyone is interested.

Paul