High Key and Low Key Lighting

High Key Lighting

High key lighting is a technique used in both films and photography that creates a lot of light onto the subject. This helps reduce contrast and creates stronger meanings and if often used in shots with infants or the elderly. High key lighting can be achieved with either studio lights or natural lighting.The use of high key lighting can soften the look of shots.

This scene from Bruce Almighty demonstrates the use of high key lighting really well and shows how the use of the lighting technique can hint towards meaning as it is when Bruce meets God, thus using the light to shows God's spiritual meaning and presence.

Low Key Lighting

Low key lighting exaggerates the contours of an object by causing darkness in certain areas while the higher point are highlighted. In film, low key lighting is often used when the director wants to isolate a subject or suggest drama. It is a common convention of the horror genre but it doesn't always necessarily mean the shot will be scary or horrific, but could be used to make the audience feel uneasy or uncomfortable. 

This scene with Bane and Batman in The Dark Knight Rises shows how effective low key lighting can be and how it is used.