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Video Production Glossary
Key Light
The key light is the first and usually most
important light that a video producer, or other scene composer will use in a
lighting setup. The purpose of the key light is to highlight the form and
dimension of the subject. The key light is not a rigid requirement; omitting
the key light can result in a silhouette effect. Many key lights may be
placed in a scene to illuminate a moving subject at certain moments.
The key light can be "hard" (focused) or "soft" (diffused), and depending on
the desired setup can be placed at different angles relative to the subject.
When part of the most common setup—three-point lighting—the key light is
placed at a 30–60° angle (with the camera marking 0 degrees). In addition to
the horizontal angle, the key light can be placed high or low producing
different effects. The most common vertical position for the key light is at
a 30° degree angle (i.e. slightly above the eye line, the nose should not
cast a shadow on the lips).
A key light positioned low appears to distort the actor's features, since
most natural or ambient light is normally overhead. A dramatic effect used
in horror or comedy cinematography is a key light illuminating the face from
below. A high key light will result in more prominent cheek bones and long
nose shadows. Marlene Dietrich was famous for demanding that her key light
be placed high.
Using just a key light results in a high-contrast scene, especially if the
background is not illuminated. A fill light decreases contrast and adds more
details to the dark areas of an image. An alternative to the fill light is
to reflect existing light or to illuminate other objects in the scene (which
in turn further illuminate the subject).
In addition to a key light, a back light may be added to "separate" the
subject from the background. When the subject and/or camera are moving or
turning around, the key light and back light may change roles.
The key light does not have to directly illuminate the subject: it may pass
through various filters, screens, or reflectors. Light passing through tree
leaves, window panes, and other obstacles can make a scene more visually
interesting, as well as cue the audience to the location of the subject. The
key light also does not have to be white light—a coloured key (especially
when used with fill/back lighting of other colours) can add more emotional
depth to a scene than full white alone. In mixed indoor/outdoor daytime
scenes, sunlight may appear to be a "warm" white, and indoor lighting to be
a "neutral" or artificially-toned white. By contrast, moonlight appears to
be "cooler" than indoor lighting.
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