Dear Radiance community,
I am comparing a measured irradiance read with a simulated one from Radiance v6.0. The shape of the output is very close, but I am confused about the unit.
Under an overcast sky, the irradiance values from the sensor are in range of 0.01-0.06 W/m2.nm (right-side plot).
But my Radiance results are in range of 10-90 (left-side plot).
What is the output unit of rtrace -co+? Shouldn’t there be a conversion factor that I missing now?
Thank you,
Nima
Although confusing and a bit non-standard, Radiance doesn’t use watts/m2.nm for irradiance. Rather, it produces values that if averaged over all the coefficients gives straight watts/m2. So, if you want to convert to watts/m2.nm, you’ll need to divide by the step size, which is (max_lambda - min_lambda)/N where N is the -cs setting.
We chose to use a coefficient average because it avoids conversions between different sampling rates and ranges.
Does this help?
-Greg
Yes it is clear now.
Thanks a lot Greg 
