mental ray Architectural and Design Visualization Shader Library

3.9 Photometric Lights 85• When intensity mode is 0, the peak intensity of the light is defined (in candela) bythe manual peak intensity cd parameter.• When intensity mode is 1, the overall flux of the light is defined (in lumen) by themaual flux lm parameter.• When intensity mode is 2, the intensity is directly derived directly from the valuesstored in the IES profile assigned to the profile parameter.distribution mode defines how the light is distributed in different directions:• When distribution mode is 0, the light is isotropic, i.e. it shines exactly the same inall directions.• When distribution mode is 1, the light is a spotlight. The light must have a spreadparameter to define the width of the beam. The distribution of light within the conefollows a cosine function, raised to the power of the spotlight cosine bias parameter.Hence, a bias below 1.0 will push light towards the edges of the cone, and a bias above1.0 will push light towards the center of the cone.• When distribution mode is 2, the intensity distribution of the light is derived fromthe values stored in the IES profile assigned to the profile parameter. Note that it islegal to combine this distribution mode with either of the manual intensity modes 0 or 1.In those cases, the IES profile is used in relative mode, trying to accomodate the desiredintensity but still accomodate the directional distribution of the IES file.Since physical lighting in real world units is highly scale dependent, the units to meter scaledefines how many scene units goes into one meter. E.g. if one scene unit is one millimeter,this would be 1000.Finally, the cm2 factor is the conversion factor between pixel values and candela persquare meter luminance values. In short, this should match the cm2 factor of themia exposure photographic shader to yield a photographically correct render, intensity wise.See also page 61.