Lighting

Lighting is used in horror films to add tension and to highlight both objects and characters. 
Different horror films also have a tone of lighting throughout their films in order to create this anxiety.
For example The Ring uses lighting in a way that makes the audience feel nervous and creates an awareness that things aren't quite right.
This is done by the green lighting hue that is used throughout the film.

Especially in this shot there is the TVs highlighted due to them emitting a light source making them brighter and stand out more, adding effectiveness to the movie, where TVs are often featured. 

From this shot we can see how the protagonist is not highlighted with light, but the main focus is on objects behind here, that are all white and are square shaped, like a TV is. 

Throughout the movie, there is no obvious light shone on the main protagonists, showing how she is losing her life as the movie progresses.

I have also found that artifical lighting is used in a way to highlight features around a setting.

For example in The Strangers, this shot has features around the room highlighted with the lighting, both the lamps and candles create a brightness in a room which creates darkness in the centre. Therefore when the villain appears this highlights him more but in a subtle way.

Here we see the protagonist in a state on panic, the lighting shone directly on her face at a little bit of a high angle highlights the sweat beads on her face showing her anxiety.