Daylight availability in Turkey

In Turkey, daylight availability data are lacking, but solar radiation data for various climatological regions have been collected regularly at meteorological stations for more than 40 years. These solar radiation data can be converted into equivalent daylight illuminance data if the luminous efficacy of solar radiation is understood.For the purpose of determining the luminous efficacy of solar radiation, an apparatus capable of simultaneously measuring exterior daylight illuminance and solar radiation was installed in the observation park of the State Meteorological Office of Ankara in 1980.The data collected during a two-year period are evaluated by a computer program, and the hourly variation of monthly, seasonal, and annual means of luminous efficacy of solar radiation are calculated, By using these values, the available solar radiation data for previous years are converted into equivalent daylight illuminance data.In this paper the hourly variation of luminous efficacy values, daylight illuminance data, and the percentages of occurrence of various illuminance levels are tabulated. The results presented here may be used to predict a design base daylight illuminance level and the possible energy savings from photoelectric control of artificial lighting installations.More reliable daylight availability data will be obtained from evaluating at least five years of records. This computer analysis will be updated each year that data are collected.