Projecting HDR onto geometry

[X14Halo]

In this video, Scott shows how to project an HDR onto geometry.
http://www.fxguide.com/fxguidetv/fxg...-mari-and-hdr/

My question is, what is the best way to apply this in Vray for Maya? Would I just stick the HDR texture onto a surface shader and have the surface shader emit the light? Or Light material, or something else? I am just starting to learn Mari, and I am very interested in getting this kind of lighting workflow going in our pipeline.

[Morbid Angel]

Yeah you would put it on a vray light material and just make sure the exposure or intensity of your hdr is correct to what your environment is. However, with that said, do not use geo lighting with hdr, it will create very strong noise. Only gi based method will give you good result.

[X14Halo]

Could you expand on that? What do you mean by "GI" based method? Are you basically saying that this workflow is bad because of all the noise it causes and it is not worth it?

[Morbid Angel]

No not bad. There is two ways to emit lighting from geometry with vray. One is to use mesh lights, which turns geometry into a geo based light source, emitting direct lighting. Similar function is available from vray light material (direct lighting). This method will create a lot of noise, so best not to use it. Instead it would be wise to use just straight up gi like irradieance map for example, this would produce best result.