Here we see the commonly used terms in lighting. Often, an art director will ask a photographer for a 'low key' or 'high key' effect, and both of these require very specific approaches to lighting. Skip the jump to find out more...
In low key lighting, dark tones predominate the image, only relieved by subtle light patches around the key features of the subject. Low-key lighting usually involves high contrast lighting with the subject positioned in front of a dark background. The main subject should be lit using directional lighting from the side, and this may be hard or soft depending on the effect required. You can use a standard reflector as the key light, sometimes fitted with a honeycomb grid. A softbox may be used if a softer source is needed, but special care should be taken here to prevent any stray light hitting the background. Smaller soft boxes and strip lights are ideal. Also fit the key light with barn doors or cutters/flags when producing this kind of lighting. This way, you can make sure only the main subject receives illumination. Any excessively deep shadows can be filled in gently using a white reflector. Try keeping the exposures on the short side (or to the left in histogram) when producing low key lighting. Half a stop underexposure is often enough to produce quite dramatic effects.
In high key lighting, light tones predominate in high key lighting, generally produced by soft, low contrast lighting with the subject positioned against a light background. The key light should be a large area light or softbox, positioned as close to the subject as possible. Contrast is kept very low, and often the mid-tones will virtually disappear. If using one main light, the background should be as close as possible to the subject to minimise light fall off or it can even be lit separately using additional flash heads. Providing the background itself is light, and the reflected light level measured by a flashmeter is between two and three stops higher than the main subject, the result will be a pure white, high key background. Shadow and mid-tone areas in the subject also need to be filled in completely, and this can be done by strategic positioning of white reflectors. If the studio walls and ceiling are painted white, they can also be illuminated using additional lamps, adding to the overall high key effect. Exposures should be on the long side, one full stop over exposure usually being enough to produce a soft, white high key image.