A soldier in one of the lever rooms will warn you about the traps, and tells you how they are associated with the lights. Alternately, you can use the summoning doll (available on the level after you jump down the pit, if you do not have it yet) to find and trigger the traps, and move your main characters up behind.
You need to learn one of the survivor trap skills before you can use the trap material. The first teachers are not available until act 2.
