High key lighting uses reduced contrast lighting that is dominated by white tones and has minimal mid-range and black tones. Often the background is white or brighter than the foreground or subject. It sets a positive or upbeat tone for the scene. It is used extensively in product shots, beauty and makeup commercials, news sets, sitcoms and film videos, especially those featuring pop artists.

High key lighting was in vogue in Hollywood during the 1930s and 1940s to overcome technical limitations as to how much contrast film could capture. Wizard of Oz made extensive use of high key lighting (although it used both three point and low key lighting in certain scenes).

High key lighting usually involves a brighter than normal key light and lots of fill lights to balance the light evenly across the scene and eliminate as many shadows as possible. Often these lights are diffused to provide softer, more even lighting. The goal is that every part of the foreground receives the same intensity of light with the background receiving a bit more light than the foreground.

A light meter can be invaluable in setting up your high key lighting—it will help you maintain even light levels across the scene.
One advantage of high key lighting is that once it is setup for a scene, individual close ups, medium shots and wide shots can be shot without additional lighting setups. This can greatly reduce the production time on shoots.

When it comes to daytime outdoor shoots, obtaining high key lighting can be challenging. The easiest way to accomplish high key lighting outdoors is to hope for an overcast day which will provide even, diffused lighting over a great area. On sunny days, large overhead diffusion panels may be used to create areas that are evenly lit. Reflectors can be used to help even out light throughout the scene.

When it comes to nighttime outdoor shoots it can be relatively easy to light the foreground, but depending on the background it can be tricky to get enough light intensity—especially if the background is an open space with lots of depth to it. A white or lightly colored wall that can serve as your background will be helpful in achieving that high key light effect outdoors at night.

To recap, you achieve high key lighting with a bright background and even lighting for your foreground subjects. The advantages are shorter setup times for individual shots once you have the high key lighting setup for a scene, and it helps reduce wrinkles in your talent and makes products pop. The disadvantages are that depth and detail are reduced and there is little dramatic mood in the scene.