This can first done in the level "Mansion", there are other opportunities later on too. (the hotel.)
In the room with the tv, left of the starting room, there's a spark. When a zombie walks through it the power shuts off.
Simply don't turn the power back on for 5 minutes and you'll get the achievement.
Apart from the surroundings being darkers and therefore harder to see the enemies, there are no additional negative side effects of the darkness to hamper survival.