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

[Majid Miri]

Hi all,


I want tosimulate skies during a period very close to sunrise and sunset when the globalhorizontal skylight is between 100 and 1 lux). 

I tried touse Daysim and Meteonorm 6.0 to create a weather data file with 1 minuteintervals, 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 asminimum. (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 Ineed to estimate the times that the skylight is less than 100 lux. 

I use Genskyto produce automatically the sky file for the times that the sun altitude isclose to horizon (below and above horizon), but it gives me much higher valuesthan I expected. I checked the IES handbook and it says that to estimatediffuse skylight (the Sky ratio method is not accurate for low solar altitude,and I guess that Gensky use the same method).

Therefore, Ireally appreciate if anyone can help me to produce a series of sky with 1minute intervals for the time the sun is very close to horizon (below or abovehorizon)


Best,

Majid


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