If the shielding angle is not correct, there is a risk of direct glare from excessively high luminance in directly radiating lamps. To avoid this, luminaires have housing parts, louvers or grids that shield the lamps. High luminance can also be reduced by upstream opal or prismatic covers. According to DIN EN 12665, the shielding angle of a luminaire is the angle between the downward-directed vertical and the direction from which the lamps and the surfaces of high luminance are just no longer visible. DIN EN 12464-1 “Lighting of indoor workplaces” defines the shielding angle as the corresponding angle in relation to the horizontal plane. Adaptation When brightness changes, the eyes need time to adjust. This adjustment process is called adaptation. The course of adaptation and thus the adaptation time are determined by the luminance at the beginning and end of the change in brightness. Adjustment from dark to light takes only seconds; it can take minutes for the eyes to adapt from light to dark. The respective state of adaptation determines visual performance.