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Topic: VRayLight units
posted by Vlado
archived on 10.11.2004
Someone was asking some time ago what are the units of intensity (the "color") for the VRayLights; finally had some time to figure that out, so here it is.
First, a few assumptions:- VRay always works with Generic units internally. VRayLights also do that and assume that 1 generic unit is equal to 1 meter. If this is not so, the multiplier of the light will need to be adjusted, if you want the light to have specific predefined intensity.
- We assume that the light color is pure white.
- We assume all other VRayLight options have the default values.
If the "Normalize intensity" option is OFF (the default), then the light multiplier defines the light intensity in watts per square meter (Watt/m^2).
If the "Normalize intensity" option is ON, then the light multiplier defines the light intensity as the total power in watts of the light source.
If the "No decay" option is ON, the light is not a physical light and exact units cannot be defined.
Some other units of measurement in VRay:- The irradiance map stores irradiance as watts per square meter.
- Pixel values represent radiance per pixel (the unit for radiance is watt per square meter per hemisphere, where 1 hemisphere = 2*pi steradians), assuming that no color mapping is performed.
Follow-ups
Q: If we are working in empirical units (1 unit = 1 foot) how should we be adjusting the multiplier? Should it just be (value X 3.2 ? What about if we check normalize intensity? Same thing? or do we need to square it for area in that case? Or should we be dividing?
A: If you have the "Normalize intensity" option ON, then you only have to specify the power of the light (in watts) - the VRayLight will do the conversion automatically. If the "Normalize intensity" option is OFF, and you want your light to emit X watts per square foot, then the multiplier should be X/(0.304^2). Again, this assumes that your Generic units are meters, while only the display units are feet. If your Generic units are feet too, then the multiplier is in watts per square foot by default.
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