Fill Light
A secondary, weaker light or reflector used to raise the shadows the key light casts, controlling contrast.
Formula / rule
Ratio = key / fill
Measured in
f-stops (EV)
In depth
Fill does not create its own shadows if it is used correctly — it should be softer, broader and weaker than the key, and placed near the lens axis so any shadow it casts falls behind the subject. A white reflector is often better than a second light, because it can only ever return light that the key already provided.
Examples in practice
A silver reflector held below the chin opens the eye sockets by a stop without adding a second catchlight.