Influence of background luminance on UGR result

The article describes UGR measurement with luminance analyzer and discusses overall impact of background luminance on the calculation result. Background luminance, defined as 2π, causes a problem if the luminance is on the periphery of the visual field. Another complication is that the position index is defined only for the upper half of the view. This causes a complication in glare measurements of luminaires in the lower part of the view. The article attempts to summarize possible variations in luminance analyzer measurements.