Low key and High key lighting

Low key 

Low key and high key lighting are terms for describing the difference in lighting on a characters face/ object that is in the scene.

This scene from blade runner is an example of low key lighting as the characters faces are light however the rest of the scene is darker particularly behind Deckard. I believe in the context of the film it's because it shows as what Deckard has been doing is ultimately evil and this links to the lighting of the film. Most of Blade runner is in lowkey lighting apart from the scenes shot in Tyrell. 

High key

The scene where Bruce meets god in Bruce almighty is a clear show of High key lighting as it emphasises the point which Morgan Freeman's character is a holy and almost other worldly being. The uses of high key lighting is to display an other worldly feeling upon the audience. 

Low key lighting can create serious moments in film whereas lowkey lighting has the ability to create unnatural feelings in film.