I rather liked this portrait I printed of model Stella The manner in which the face recedes into the shadows creates a sense of mystery as the model's features are partially obscured. I was attempting to suggest the model's beauty rather than clearly delineate it.
But is this a "low key portrait" or an example of "low key lighting"? There is a difference between the two that is sometimes confusing. The Wikipedia entry on "low key lighting" is so short that it can be quoted in its entirety:
"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. Low-key lighting often uses only one key light, optionally controlled with a fill light or a simple reflector.
"Low key light accentuates the contours of an object by throwing areas into shade while a fill light or reflector may illuminate the shadow areas to control contrast. The relative strength of key-to-fill, known as the lighting ratio, can be measured using a light meter. Low key lighting has a higher lighting ratio, e.g. 8:1, than high-key lighting, which can approach 1:1.
"The term 'low key' is used in cinematography to refer to any scene with a high lighting ratio, especially if there is a predominance of shadowy areas. It tends to heighten the sense of alienation felt by the viewer, hence is commonly used in film noir and horror genres."
Fair enough, but Wikipedia then draws a distinction in its definition of "low key":
"Low key as a term used in describing paintings or photographs is related to but not the same as low-key lighting in cinema or photography.
"A painting or image is low key if its dominant values are dark."
The source of the confusion may lie in the fact that the term "low key" antedates the invention of photography and cinema and the use of artificial lighting. There is an article in Photography - Stack Exchange that thoroughly explores the history of the terminology and makes for interesting reading.