[Radiance-general] Conversion of RGB irradiance values to a illuminance value

[Christopher Rush]

If I understand your situation correctly, I believe you would need to know the reflectance of the material at the point of the irradiance measurement to backtrack to illuminance for calibration. This works when the surface is Lambertian (diffuse), and much more difficult if there's any glossiness. For calibration purposes, people often include a photographic grey card of known reflectance in their scene and take actual luminance or illuminance meter measurements at the grey card.

From: Claus Brøndgaard Madsen [mailto:cbm at create.aau.dk]


I use hemi-spherical HDR images to compute a vertical irradiance value (W/m^2) for each color channel.

If I wish to compare/calibrate these numbers to a reading from a light meter (giving illuminance in Lux) how do I go about converting the three (RGB) irradiances to illuminance?

Cheers,
Claus

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