High-key lighting is a style of lighting for film, television, or photography that aims to reduce the lighting ratio present in the scene. This was originally done partly for technological reasons, since early film and television did not deal well with high contrast ratios, but now is used to suggest an upbeat mood. It is often used in works of comedy. High-key lighting is usually quite homogeneous and free from dark shadows. The terminology comes from the higher balance in the ratio between the key light and the fill light in a traditional three-point lighting setup.
In the 1950s and 1960s, high-key lighting was achieved through multiple light sources lighting a scene—usually using three fixtures per person (left, right, and central)—which resulted in a uniform lighting pattern with very little modeling. Nowadays, multiple hot light sources are replaced with much more efficient fluorescent or LED soft lights, which provide a similar effect.
