High Key lighting involves the fill lighting, used in the three point lighting technique, to be increased to nearly the same level as the key light itself. This extra illuminated light can make a scene appear very bright and soft, also showing very few shadows.
This particular lighting technique can be found in musicals and comedies, especially in the classic Hollywood era of film.

An example of this high-key lighting was from the film “The Wizard of Oz” (1939). It created a very bright, soft and vibrant look in the image.