References(10) Cited-By(8) The standard value of the horizontal illuminace from unobstructed sky has not been yet established in Japan for the calculations of the daylighting and PSALI, though it is the most essential and fundamental for the energy conservation in the field of lighting design. A great deal of data on the horizontal illuminance from unobstructed sky have been gathered for several years by the authors when they tried to measure the luminance distribution of the sky under various conditions; the data cover not only almost whole seasons through a year and various times within a day, but also different meteorological conditions. Based upon those data, a proposal on the values of the horizontal illuminance from unobstructed sky at the selected standard point (35°N, 135°E) has been made by the statistical analysis and research investigations, following the values at Nagoya, related to the percentage of the available hours to many kinds of the designed working duration, such as 9 a.m. to 5 p.m. This proposal has been considered very reasonable and useful for the calculations of daylighting and its applications, so it has been extended to be applied in all over Japan. Furthermore the method developed by this research work and the results stated in this paper have convinced the authors of their world-wide applicability.
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