The effect of luminaire type and spacing on visibility levels in unobstructed spaces

The authors examine how luminaire type and spacing affect task contrast and visibility levels in unobstructed office spaces. The Lumen-Micro program was used to calculate visibility levels in a model open-office space as a function of luminaire candle-power distribution, fixture spacing, and illuminance level. Three representative luminaires were parametrically examined: a lensed troffer, a high-performance parabolic, and a high-performance uplight. Small differences in average task visibility levels were observed for the different luminaires and fixture spacings examined, but these differences were slight compared with variability within an installation. The study indicates that if one does not know the location of the task a priori, then it is not possible to achieve consistently high visibility levels throughout a space without resorting to lighting solutions that are intrinsically inefficient