VrayLightMtl multiplies Light Color by Opacity even without checkmark

[im.thatoneguy]

The Vray Light Material always multiplies light color output by Opacity regardless of the flag to do so or not.

So completely transparent light emitting materials are not possible. Closest you can do is set Opacity to just above black 0.005 and then set the output amount to Amount*200.0 which dramatically slows sampling.