Is lighting really that important? Ask any Cinematographer (DP, Director of Photography. It is essential, vital, paramount – YES IT IS!
A cinematographer or director of photography (sometimes shortened to DP or DOP) is the chief over the camera and light crews working on a film, television production or other live action piece and is responsible for making artistic and technical decisions related to the image. The study and practice of this field is referred to as cinematography. (wikipedia.org)
If you even remotely interested in film and/or filmmaking I would strongly recommend watching Visions of Light.
Film lighting has three main purposes. The first is clarity of image. It is important for viewers to be able to discern all the important elements in the frame. These might range from facial expressions and physical gestures to the presence of significant props. In early cinema this was the sole purpose of lighting, but around 1905 other factors came into play. Lighting’s second purpose is a quest for greater realism. Films began to introduce visual schemes that suggested that the lighting came from logical sources within the world depicted. The use of “effects lighting,” as it was known at the time, paved the way for the third purpose: the creation of atmosphere or emotional effect. The development of lighting technique as a significant element of mise-en-scène became an important tool for manipulating audience responses to characters and narrative events. Increasingly, a repertoire of standardized lighting techniques came to be used for particular dramatic situations and particular lighting styles came to be strongly associated with film genres.