Keywords: sky luminance, zenith luminance, daylight, CIE, illuminance, irradiance.

The sky condition classification is important to evaluate the performance of daylight and estimation energy savings in buildings. Sky luminance distribution depends on the sky condition classification. This distribution, is used in most of the lighting simulation programs for the assessment of daylight quality in buildings. The computer program which calculates sky luminance using the Perez Sky Model is used in the Republic of Korea [1]. However, sky luminance depends strongly on the weather conditions, solar altitude and position. Predicting sky luminance is not accurate and estimates of the range of errors are required. Furthermore, actual measurements of sky luminance are difficult. Recently, sky luminance data were measured and analysed in Hong Kong, Singapore and Bangkok [2,3,4]. Unfortunately, the daylight measurement data are still not measured under the real sky in Korea.

Therefore, this study is to validate the sky luminance measurement system according to the CIE quality control test, based on the CIE Guide to Daylight Measurement [5]. The aim of this paper is to validate the sky luminance measurement system using the CIE quality control test. For this study, sixteen parameters of daylight measurement systems were established based on the CIE Guide to Daylight Measurement. The sky luminance was measured using a Sky Scanner EKO, model MS-321 LR. A sky scanner MS-321LR tracks 145 points of the sky hemisphere. Measurement of the 145 points is based on the CIE108-1994 recommendations. The sky luminance measurement system is located on the rooftop of the Kyung Hee University of South Korea (37.24°N, 127.07°E).

As a result, four QC tests were conducted to test the effectiveness of the sky luminance measurement system and a high accuracy at 100% was found. In other words, the sky luminance measurement system of Kyung Hee University is believed to provide sky luminance data that is both reliable and conforming to CIE standards. Therefore the Kyung Hee University daylight measurement system is reliable and the measurement data would be useful for further daylight research.

1

K.D. Song, S.M. Han, "Developing Databases of External Illuminance and Sky Luminance Distributions for Building Daylighting Design", Journal of the Korean Society of Living Environment System, 6(2), 58-65, 1999. (in Korean)

2

D.H.W. Li, "Evaluation of overcast-sky luminance models against measured Hong Kong data", Applied Energy, 70, 321-331, 2001. doi:10.1016/S0306-2619(01)00044-7

3

S.K. Wittkopf, L.K. Soon, "Analysing sky luminance scans and predicting frequent sky patterns in Singapore", Lighting Research and Technology, 39(1), 31-51, 2007. doi:10.1177/1365782806070683

4

S. Chirarattananon, P. Chaiwiwatworakul, "Distributions of sky luminance and radiance of North Bangkok under standard distributions", Renewable Energy, 32, 1328-1345, 2007. doi:10.1016/j.renene.2006.06.004

5

Commission Internationale de l'Eclairage(CIE), "Guide to recommended practice of daylight measurement", CIE TC 3-07, 1994.

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