[Radiance-general] Gendaylit Visible radiation

[Jan Wienold]

Hi Julien,

Using  the default option (-O 0 ) gendaylit "transfers" the solar 
radiation into visible radiation, using a luminance efficacy model.
Therefore the "sky irradiation" (=equals visible irradiation) differs 
also from situation to situation. The luminance efficacy of the sun is 
much lower than for the sky and this is taken into account by the model.

So for your case

gendaylit 6 21 12:00GMT -a 46.51 -o -6.56 -m -15 -G 500 200

you get
425 W/m² visible radiation

if you use

gendaylit 6 21 12:00GMT -a 46.51 -o -6.56 -m -15 -O 1 -G 500 200
you get
695 W/m² solar radiation  which is +- the input radiation of 
500+200=700W/m²

So the results are as expected.

The included luiminance efficacy model works properly within gendaylit - 
at least a recently internal performed validation study on measured data 
showed this.

By the way, my colleague will announce later today a major update of 
gendaylit, which have some significant improvements included.

Cheers,

Jan



On 01/31/2013 11:56 AM, Julien Boutillier wrote:
> Hi everyone,
>
> I 'm using gendaylit function to generate sky with visible spectrum only. I introduce horizontal direct irradiance and horizontal diffuse irradiance (-G parameter) which are computed from horizontal global irradiance (meteo data : full spectrum).
>
> I don't understand why sky irrandiance in Radiance is approximatively 60% of horizontal global irradiance. In my mind, the visible spectrum is approximatively 40-45% of full spectrum, is it wrong?
>
> Example gendaylit command :
> 	
> 	gendaylit 6 21 12:00GMT -a 46.51 -o -6.56 -m -15 -G 500 200
>
> Thanks for your answer.
>
> Cheers
> Julien
>
>
>
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-- 
Dr.-Ing. Jan Wienold
Head of Team Passive Systems and Daylighting
Fraunhofer-Institut für Solare Energiesysteme
Thermal Systems and Buildings
Heidenhofstr. 2, 79110 Freiburg, Germany
Phone: +49(0)761 4588 5133 Fax:+49(0)761 4588 9133
jan.wienold at ise.fraunhofer.de
http://www.ise.fraunhofer.de

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