Photographic lighting is the illumination of scenes to be photographed. A photograph simply records patterns of light, color, and shade; lighting is all-important in controlling the image.
Perceptual Cause and Effect
Lighting creates the 2D pattern of contrast the brain interprets to recognize 3D objects in photographs. In an in-person viewing experience, the brain relies on stereoscopic vision, parallax, shifting focal in addition to the clues created by the highlight and shadow patterns the light on the object creates. When viewing a photo, the brain tries to match the patterns of contrast and color it has seen to those other sensory memories.
«The baseline for what seems "normal" in lighting is the direction and character of natural and artificial sources and the context provided by other clues»
The Natural Light Baseline
To differentiate that role from that of "key" modeling when a modeling source moves behind the object, it is typically called a "rim" or "accent" light. In portrait lighting, it is also called a "hair" light because it is used to create the appearance of physical separation between the subject's head and background.
When a photographer puts the sun behind an object, its role in the lighting strategy changes from modeling the front of the object to one of defining its outline and creating the impression of physical separation and 3D space a frontally illuminated scene lacks.
To differentiate that role from that of "key" modeling when a modeling source moves behind the object, it is typically called a "rim" or "accent" light. In portrait lighting, it also called a "hair" light because it is used to create the appearance of physical separation between the subject's head and background.
Creating Natural Looking Artificial Lighting
A typical studio lighting configuration will consist of a fill source to control shadow tone, a single frontal key light to create the highlight modeling clues on the front of the object facing the camera over the shadows the fill illuminates, one or more rim/accent lights to create separation between foreground and background, and one or more background lights to control the tone of the background and separation between it and the foreground.
There are two significant differences between natural lighting and artificial sources. One is the character of the fill and the other is a more rapid fall-off in intensity. In nature, skylight fill is omni-directional and usually brighter from above. That "wrap around" characteristic is difficult to duplicate with a directional artificial source.