Effects of Lighting

Lighting in film is an extremely effective way to get a point across without using words. Low key lighting can make characters seem sinister very easily or just make scenes far more dramatic, whereas high key lighting can bring eeriness to a new level.
The eerie effect of high key lighting is most effectively demonstrated in the movie Fargo by the Coen brothers. At several key points during the film, the Coen brothers take a long shot from a high angle in high key lighting with snow all around, and the effect is one of a kind. This kind of shot is part of what Fargo is known for, and a large reason for why I consider Fargo the Coen brothers' best piece of work.
The sinister effect of low key lighting, on the other hand, is shown in the movie we all just watched, Citizen Kane. One good example is when Kane is signing his Declaration of Principles, his face is completely in shadow, giving him a crueler visage than that of Bernstein and Leland next to him in the light. This foreshadows Kane's eventual turn to reporting dishonestly. Another example of low key lighting in Citizen Kane is the scene in which Kane tells Susan in no uncertain terms that she will continue singing. Kane towers over her and his shadow lies imposingly upon her entire body, not making her look sinister, but more weak and helpless.
So basically both high and low key lightings have different effects, and when used correctly are very good at producing those effects.