A creature that has darkvision can see normally regardless of light. It ignores concealment that is a result of dim light or darkness.

Published in Monster Manual 2, page(s) 217, Monster Manual, page(s) 281, Player's Handbook 3, page(s) 220, Rules Compendium, page(s) 310, Monster Vault: Threats to the Nentir Vale, page(s) 122.