Uniform lighting, whether by natural daylight or by artificial lighting, is important where there is a requirement to operate in an environment with significant differences in lighting levels.

Changes between well and poorly lit areas, especially where glare occurs, can cause significant eye discomfort, leading to stress and tiredness and therefore potentially jeopardizing safety as the human eye takes its time to adapt to changing lighting conditions.

The uniformity factor can be expressed as a ratio of the highest to lowest illuminated area in a given room or space. The closer it is to one, the more uniformly lit the space is. It is therefore the design of the daylighting rather than a function of the rooflight itself. Increased rooflight areas with high diffusion and lower light transmission levels provide the most uniform lighting, or highest uniformity factors.