[Radiance-general] accounting for irradiance due to ultraviolet in rtrace

[Lars O. Grobe]

Hi!
> @Lars: do you mean like this? rcalc -e '$1=($1*0.33+$2*0.33+$3*0.33)' or rcalc -e '$1=0.4*($1*0.265+$2*0.67+$3*0.065)'

None of the above... ;-)

I recommend setting all three channels to the same value. E.g. if a diffuse surface reflects 50% of UV radiation, I'd use

void plastic diffuse50
0
0
5 .5 .5 .5 0 0

Of course you must have defined what wavelength range to consider. And apply that to all materials, sources, and interpret the results. Then, the result of any channel can be taken, or, in rcalc terms, $1=$1 and $1=$2 and $1=$3 should all be valid.

> ? the factor of 0.4 comes from dividing the wavelength spectrum of UVR (120-400nm) to PAR (400-700nm)...

I did not understand this, but probably you do not want this...

So maybe to explain things, Radiance is a raytracer that outputs results in watts, which implies that you define some wavelength range. To make life easier for lighting applications, it calculates three ranges in parallel, and most people use this for red, green and blue. What I recommended is, as you have only one range that you are interested in, to set the first channel to UV. This will be the only channel you are interested in. Only to be on the safe side, set the second and third channel to the same values, to avoid strange effects due to weighting. Still you use only one channel, and no multiplications using rcalc.

Ah, and please get a copy of Rendering with Radiance. It will be very helpful!

Cheers, Lars.