A study on the estimation of the relative frequency of occurrences of the Clear Sky, the Intermediate Sky and the Overcast Sky in Japan

• Published in: Journal of Light & Visual Environment Vol. 9; no. 2; pp. 2_22 - 2_31
• Main Authors: NAKAMURA, Hiroshi, OKI, Masato, HAYASHI, Yutaka
• Format: Journal Article
• Language: English
• Published: Tokyo The Illuminating Engineering Institute of Japan 1985; Japan Science and Technology Agency
• ISSN: 0387-8805; 1349-8398
• DOI: 10.2150/jlve.9.2_22

The Mean Sky11)13)15∼18) and the Average Sky20∼22) have been proposed for new daylighting design methods which conform with the real sky conditions more closely than the conventional methods based upon the Uniform Sky*01, the CIE Standard Overcast Sky1) and so on. In order to compose the mean Sky*02) proposed by the authors at any geographical point in the world, the luminance distribution of all the sky conditions which really appear there are to be divided conveniently into three types, that is, the Clear Sky, the Intermediate Sky and the Overcast Sky, and their luminance distribution is to be defined respectively14), and moreover, their relative frequency of occurrences within the total working hours is indispensably to be estimated. In this paper, the relation between the three Skies and the meteorological observation data recorded regularly in Japan is described, and a procedure is stated which has been developed in order to estimate the relative frequency of occurrences of the three Skies from the meteorological observation data, and finally, the yearly relative frequency of occurrences of the Clear Sky, the Intermediate Sky and the Overcost Sky relating to the usual working duration in Japan*03 is assumed to be 5%, 70% and 25%, respectively, as the result of this research work.