Do I understand correctly that you want to essentially texture the directional emission of the light sources? All renderers already provide texturing the radiosity at any point on the light source surface. What streamline900 seems to want is the ability to also control the radiance emission at each point, i.e. the directional distribution. As far as I know, IES profiles only texture the intensity, not the color, right? I guess this could be achieved by attaching a (hemi-)spherical map to the light source. I find this a pretty reasonable feature request, and I can imagine that interesting results can be achieved with this. Does any other renderer have such a feature?