vrayLightMtl

vray materials: Apparently glass/transparent materials only work in blend when used as a base.

vray light materials limitations: The direct illumination options currently only work properly if the VRayLightMtl material is the only material applied on the object. They will not work if the material is part of a complex material like a Multi/sub-object material or a VRayBlendMtl material. This restriction will probably be removed in a future release

tested it out by applying a black and white map in to opacity input. but it didn't work. my results was ended up with a completely white vrayLightMtl.(something like surfaceshader)
however it works when i placed the same exact map in to both diffuse and opacity slot. Transparency/Opacity works.

When direct illumination was switched on, opacity map got broken again. ><
Not sure if it's some bug in for vrayLightMtl or not..