[Radiance-general] Creating sky files for low solar altitudes

[Majid Miri]

Hi all,
I want to simulate skies during a period very close to sunrise and sunset when the global horizontal skylight is between 100 and 1 lux).I tried to use Daysim and Meteonorm 6.0 to create a weather data file with 1 minute intervals, but both of them are based on watt and their minimum value is 1 watt. When converting from irradiance to illuminance, it gives me around 140 lux as minimum. (I use “gendaylit.exe 3 21 12.0 -a 59.7 -o -18.0 -m -15.0 -W 0.0 1.0 -O 2“ to create a sky with only 1 watt horizontal diffuse irradiance)
However I need to estimate the times that the skylight is less than 100 lux.I use Gensky to produce automatically the sky file for the times that the sun altitude is close to horizon (below and above horizon), but it gives me much higher values than I expected. I checked the IES handbook and it says that to estimate diffuse skylight (the Sky ratio method is not accurate for low solar altitude, and I guess that Gensky use the same method).Therefore, I really appreciate if anyone can help me to produce a series of sky with 1 minute intervals for the time the sun is very close to horizon (below or above horizon)
Best,Majid
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