Vertical Illuminance Measurement for Clear Skies in Tehran

To effectively design daylight in buildings, daylight availability data are necessary. Although there is a great potential for daylight energy in Iran, its use has been hampered by the absence of measured data. In this paper the illuminance data on the vertical south facing surfaces of Tehran were estimated using the IESNA model. For this propose an illuminance measuring set was used in order to measure the vertical illuminance for standard times over 17 days at one minute intervals from 9 a.m. to 4 p.m. Then, the measured data were compared with the IESNA model calculated data. A regression model between measured and calculated data was developed, which showed an acceptable linear correlation (r2=0.9535). Also mean hourly and monthly vertical illuminance was obtained from the new equation between measured and calculated data for a whole working year. To estimate daylight availability, Iso- Klx lines for working hours and frequency curves for vertical illuminance on south facing surfaces were produced.