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.

Low–key lighting is a style of lighting for photography, film or television. It is a necessary element in creating a chiaroscuro effect. Traditional photographic lighting, three-point lighting uses a key light, a fill light, and a back light for illumination.

These are my examples of high and low key lighting. the image of the left is very dark and a very loft light has been used to take this image whereas the photo on the right is a very bright nearly over exposed due to a very bright harsh light source.