Ceiling-based luminance measurements: a feasible solution?

Luminance distributions would be very suitable as input for lighting control systems that aim for a comfortable lit indoor environment. Luminance distribution measurements should then correspond to the visual field of the user. However, this will interfere with office activities. Therefore, this study aims to validate whether it is feasible to approximate the luminous conditions experienced by the user using ceiling-based measurements instead. The average desktop luminance was measured using a luminance camera, under varying conditions, simultaneously from eye level and ceiling and their relations were analysed. Normalized root mean square errors were found ranging from 10,3 % to 14,3 %, while the average bias was 14,2 % between measurements from eye level and ceiling. Based on these results, it is concluded that the experienced desktop luminance cannot be exactly replicated by ceilingbased measurements. However, ceiling-based luminance measurements are able to provide a reasonable approximation that suffices for practical systems. Keywords: Luminance Camera, Field of View, HDR, Ceiling-based, Luminance distribution, Desktop luminance, Unobtrusive measurements