The definition of low key lighting is a filmic lighting style that uses a hard source to encase your scene in shadow. Low key lighting wants contrast and blackness.
Low Key Lighting:
Dark tones, blacks, shadows
Striking contrast images
Used in noir or thrillers for ominous warnings
What is a Fill Light?
A fill light cancels out the shadows created by the key light. A fill light is placed on the opposite of the key light, and usually not as powerful as the key.
Fill Light Summary:
Remove shadows created by the key,
Does not create shadows or it’s own characteristics.
What is a Backlight?
A backlight hits an actor or object from behind. It is placed higher than the object it is lighting. Backlights are used to separate an object or an actor from a background. They give more shape and depth. Backlights help the frame feel three-dimensional.
Back Light Summary:
The sun is a great backlight – you can use a reflector or bounce the sun at a lesser intensity back the subject.
If a backlight is placed behind an actor at an angle, the backlight is called a “kicker.”