This is imposition of quality on the scarcely visible air through which objects and people are seen. One rule of lighting maintain the visibility and ambiance (the surrounding atmosphere) must be inherent to the total theatrical design, including scenery and costumes.
Light affects what we see, how we see, how we feel, and even how we hear.
Lighting is the combination of science and art. Science being the understanding of the technology in the making of lighting instruments and equipment and the art being the creative use of such instrunents and equipment.