Thanks Michal,
Yes, I'm aware of the option to use LightMaterial, but since we want to be able to incorporate the powerful Vray LightMix workflow it becomes impossible to use LightMaterials this way, because it either creates hundreds LightMix layers (one for every luminous material) quickly caping the limit of 64 layers for LightMix, or it merges them all in one big layer which is useless in post editing.
Ehh, if there only was some other 3dsmax container type suitable for the job...
Let's hope in future vray versions there'll more flexible solution for LightMaterials in LightMix.
Anyway, thanks for the info and best regards.
Przemek