Light Profiles

lightprofile "name"
    format ies
    file "filename"
    [ flags flags_int ]
    [ hermite degree_int ]
    [ resolution xres_int yres_int ]
end lightprofile

Light profiles such as IES or Eulumdat are files supplied by lamp vendors to describe their products. They contain a mesh of measured light intensities. The light profile block in the scene file allows loading a light profile file on disk, and converting the data into an internal format that is efficient for lookup in light shaders using the mi_lightprofile_sample (or mi_lightprofile_value) shader interface function.

The only supported light profile format supported at this time is IES and Eulumdat. Other formats such as CIBSE may be supported in later versions of mental ray. The format statement may not be omitted.

The file statement names the file supplied by the lamp vendor.

The flags statement can be used to override the horizontal sample order in an IES file. There are two IES file types in common use, type B and type C. The IES standard defines that samples are stored in counter-clockwise order. Type C files conform to this standard, but about 30% of the type B files deviate from the standard and store samples in clockwise order, without giving any indication in the IES file that mental ray could use to switch the order. (Sometimes there is an informal comment.) If flags is 1, mental ray assumes clockwise order contrary to the IES standard for these incorrect type B files. If flags is 2, mental ray assumes the normal counter-clockwise order. Type A IES files are not supported. Flags have no effect on Eulumdat light profiles.

At this time only linear and cubic interpolation ( hermite 1 or hermite 3) are supported. The resolution statement defines the precision of this interpolation by specifying the number of points on the smoothed mesh; for linear interpolation it always matches the resolution of the sample mesh in the profile file.