Disability glare occurs when visibility is impaired due to excessive brightness. This can occur when light scatters in the eye in such a way as to put a veil of luminance across the retina. A simple test for veiling reflections is to place a mirror on the visual task. If the image of any light source appears in the mirror, then veiling reflections are present. The lighting professional learns how to position lighting equipment to avoid glare.
Psychological needs are another aspect of the lighting quality issue.
Many designers rely on research performed in the 1960s by lighting expert John Flynn of the Pennsylvania State University. Flynn affirmed people's moth-like attraction to light, a phenomenon designers use to indicate building entrances or attract people's attention to merchandise displays. More importantly, though, Flynn linked lighting configurations to the subjective impressions people form about a room. For example, he determined that if the perimeter of a space has a high, even luminance, people tend to perceive the space as being larger than the same space without the high perimeter luminance. Similarly, he established that a feeling of privacy is enhanced if the lighting designer provides low luminance near the user and higher, non-uniform luminance patterns remote from the user.