Lighting

In Horror/Thriller films the lighting it generally dark. Most horror films have dark lite scenes when something is about to happen. 

 Dark lighting is also used to identified a antagonist. The dark light makes scenes feel more tense because you don't know what is in a room or where something or someone is because it is dark. It can also hide things like faces to create a scenes of mystery.

The use of colored lights to connote something is also sued in horror and thriller e.g. red can connote danger or blood.