[Radiance-general] Weighting factors used in the irradiance calculation

[Jan Wienold]

Hi Parisa,

in fact these are weighting functions derived from v(lamda). So you 
should use them only when  all your quantities are in photometric units. 
Irradiance "usually" implies the solar spectrum, but in RADIANCE this 
is  used also only considering the visible spectrum (and then using the 
weighting). I'm not sure if a color weighting makes sense when talking 
about radiometric quantities using the solar spectrum. Usually I 
calculate everything in "grey" (r=g=b) when using the radiometric 
quantities, so this problem doesn't occur. Be aware, that you usually 
calculate everything in photometric quantities in RADIANCE, so if you 
want to calculate the solar spectral behavior you have to take care of 
using the related values(solar transmittance for glazing, solar 
reflectance of surfaces and generate sky and sun with radiometric 
quantities). As far as I know only if you use gendaylit with the -O 1 
option, then sky and sun are automatically in radiometric quantities 
(which means your results are in W/m*m solar spectrum).

Jan

Am 6/22/15 um 5:50 PM schrieb parisa khademagha:
>
> Dear all,
>
>
> I have two questions regarding the weighting factors (0.265, 0.670, 
> 0.065) that are used in the formula ( I = 0.265 I_R + 0.670 I_G + 
> 0.065 I_B ) with which one can convert the spectral irradiance triad 
> to irradiance. My first question is: where these weighting factor come 
> from? Do they incorporate the spectral sensitivity of the human eye 
> (so called V(λ)) in the irradiance calculation? My second question is: 
> should the summation of these weighting factors be always equal to 1.
>
>
> Thank you in advance,
>
> Parisa
>
>
>
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-- 
Dr.-Ing.  Jan Wienold
Ecole Polytechnique Fédérale de Lausanne (EPFL)
EPFL ENAC IA LIPID

http://people.epfl.ch/jan.wienold
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Phone    +41 21 69 30849

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