Rim Light
A light placed behind and to one side of the subject that draws a bright edge along its outline, separating it from the background.
Measured in
f-stops (EV)
In depth
Rim light works because separation is a matter of edge contrast, not overall brightness — a dark subject on a dark background reads clearly the moment its outline glows. It is usually set half a stop to two stops above the key, and it must be flagged carefully or it will spill into the lens and cause flare.
Examples in practice
A gridded strip light behind the subject's shoulder puts a thin bright line along the hair, lifting it off a black backdrop.