For the luminance measurements reported in the present work, one sensor was used to measure zenith luminance, and 34 sensors were positioned on a dome with their collimators pointing toward different positions P on the celestial sphere, which can be specified by the values of their zenith Z and azimuth 0 angles. Overcast skies values were used. The final model proposed for the mean luminance distribution for overcast skies normalized to the zenith luminance L-Z theta/L-z has been developed in four steps. For each value of Z, the mean value of L-Z theta/L-z is expressed as a ratio of gradation functions that depend on theta. Only for 0 = 180 degrees, a good coincidence is obtained with the model proposed by the Commission International de l'Eclairage (CIE) for a wide range of values of Z. (c) 2005 Elsevier Ltd. All rights reserved.