Low-key Lighting
A lighting approach in which most tones sit in the lower half of the range, with a small lit area surrounded by darkness.
In depth
Low key depends on subtraction as much as illumination: the key is usually small, gridded and close, and flags and black panels keep light off everything else. The technical challenge is separation — without a rim light or a slight background lift, a dark subject disappears entirely into a dark ground.
Examples in practice
A gridded strip light on one side of a face, with black flags opposite, leaves ninety per cent of the frame in shadow.