In the previous report, every 5% of average sky luminance distribution of the accumulate frequency of occurrences was obtained by every 5 degrees of solar altitude. The luminance distribution of the average sky was classified into five categories of the clear sky, the near clear sky, the intermediate sky, the near overcast sky, and the overcast sky, However, this method can not be applied when the sky, luminance distribution is not measured. It is necessary to develop a method to estimate sky luminance distribution based upon other data gained easily in order to provide sky, luminance distribution as the basic data of the daylighting design. The relation between the quantities concerned the daylight and the classified sky luminance distribution was examined, Finally the value of horizontal global illuminance multiplied optical airmass and divided by extraterrestrial illuminance was selected as the index shown the correlation with the sky luminance distribution.