Luminaire RGB values and total lumens

Hello Radiance community, I’m trying to better understand how Radiance handles RGB values of a luminaire in relation to the ‘total lumens value’ that’s provided from an ies file. Does Radiance scale luminaire RGB to match the total lumens value? if so, how is this adjustment done?

Any clarification or references I can check out would be greatly appreciated.

Belal Abboushi

Hi Belal,

The code is in src/cv/ies2rad.c. If I remember correctly, the total lumens value (if present) is ignored on the input. Instead, the candela values are multiplied against any depreciation factor or multiplier provided, and this goes directly into computing the output intensity for the luminaire. The conversion from candelas to watts/sr./meter^2 involves the projected area of the light source (so may have a cosine factor) and the Radiance-standard 179 lumens/watt conversion factor.

The whole process is a bit complicated and I don’t remember it off the top of my head. Some details are also found in the ray/src/cv/ file.