The normal illumination by the direct sunlight outside the earth's atmosphere, is one of the most basic quantity in daylighting. It has been believed up to this time in our country that the value is 150, 000 lx. But this is the very old data, so the value should be renewed to-day. This report is the study on this subject over the wide spread literatures. The resultant value is reported 142, 000, lx.
