Feasibility of ceiling-based luminance distribution measurements

There is a high relevancy in the luminance distribution related to the perceived visual comfort. Moreover, the required technology is maturing such that it is feasible to integrate such devices in lighting control systems, which is expected to improve the overall lighting quality in office environments, or to conduct long-term field studies. Preferably, the luminance distribution measurement corresponds to the visual field of the user. However, for long-term measurements this is not feasible as this causes interference. Therefore, this study aimed to find a suitable ceiling-based position for luminance distribution measurements. In a first phase, the most suitable ceiling-based measurement position was identified for four luminance based metrics: Desktop Luminance, Monitor Luminance, B40 Luminance, and Retinal Illuminance. The results showed that a ceiling-based position above the aisle with a 20° angle relative to the ceiling was the most suitable position because its field of view has large similarities with the field and angle of view of the user. In a second phase, the performance of this most suitable position found in phase 1 was assessed under real office conditions, and compared with the visual field of the user. The Desktop and Monitor Luminance achieved an acceptable accuracy with very basic commissioning. The Retinal illuminance was measured with a reasonable accuracy when an elaborate calibration procedure was applied. For the B40 Luminance, in all scenarios, inaccuracies above 20% were found. This study shows that ceiling-based measurements are feasible, except for the B40 luminance, however, one should account for the introduced uncertainty.