Ceiling with indirect lighting
With indirect lighting the average luminance on the ceiling should not exceed 500 cd/m². Within limited areas of the ceiling, a maximum luminance of 1500 cd/m2 is acceptable. The gradient or luminance transition must not be overly sharp so that the lighting in the ceiling is not perceived as distracting and uneven. Luminance uniformity (Lmin/Lavg ) should not exceed 1:10.
With background lighting on walls, the maximum luminance should be limited to 1000 cd/m2 .
However, studies show that, with a horizontal illuminance on a working area of 500 lx, illuminance on the ceiling of 250–500 lx is perceived as comfortable. The ratio between the ceiling and working area should be 1:1 or 1:2. At the same time, studies show that light distribution from the luminaire of 50-50 is often preferable. This entails a luminaire with 50% direct light and 50% indirect light.