Shadows play an important role for the perception of spatial structures and perspective, and for general orientation. Good shadow conditions are created through an appropriate mix of diffuse (non-directional) and directed light (Ten Guidelines for Right Light). This ensures a gradual transition from dark to light areas. The actual mix depends on the visual tasks and activities involved. Completely diffuse light without any shadowing causes a loss of plasticity and creates an impression of monotony. Equally, shadows that are too harsh restrict visual performance because of the pronounced differences in luminance and thus limit the assimilation of visual information, too. It may alsobe the case that significant areas of the visual field receive no light at all, with all the attendant safety risks that implies. As yet no satisfactory parameter has been devised to evaluate shadow conditions.

In the case of ambient lighting, shadow conditions can be assessed as the ratio of cylindrical to horizontal illuminance (Ez / Eh).

Excessively harsh shadowing can be avoided by ensuring that the ratio is no lower than 1:3 at 1.2 m above the floor (DIN 5035 Part 1). Shadows that are too deep can be softened through the appropriate arrangement of luminaires with a wide-angle Intensity Distribution Curve and the use of bright finishes for walls and furniture.