Photography is a medium of light; the name itself means to write or record (graph) with light (photo). Great photographers know how to control light, even in the field, when they have to rely on available light. They do this through angle and framing, and through exposure. Sometimes they employ reflectors when possible.
Photographers strive for light that looks “natural,” if only to a specific genre. Those who create video games have made a science of mimicking light as it is seen in photography. They categorize light according to how diffuse or concentrated it is.
Lighting can be flat or create brilliant reflections and dramatic shadows. Light can appear to come from an obviously artificial source, or a photographer can carefully conceal the source. All these affect how we view a photo and judge its veracity.