vray light mtl and gi shadows.

[super gnu]

i often use geometry with a lightmtl on for filling spaces with generic light. its very useful for doing loads of rooms in a tower, for example, as with a material by element and a multisubtex, you can get some nice random colours very easily.

also useful for doing office floors where there are thousands of cieling lights.

i usually have the geometry invisible to camera and reflections, with all shadowcasting off.

however there is one thing that has always bugged me: how to stop the damn geometry casting a gi shadow on the cieling?

if the plane is close to the cieling, you get a dark spot above it as it occludes the bounced light. ive tried turning off "recieve gi" but it doesnt help. obviously i cant turn off "visible to gi" as then it wont emit any light.

i sometimes faff around putting another weaker lightmtl on the back of the geometry to act as a fill light, but it never looks good.

only real solution is to move the geometry away from the cieling.. making the shadowing more subtle. however this then means the light is coming from too low in the space, creating its own issues.


any suggestions? how to make geometry with a lightmtl on emit gi, but not occlude gi rays?

[super gnu]

thinking about it, it is tricky since the light from the geometry comes from gi rays hitting the geometry, not the other way round as in direct light.

if we allow rays to pass through as if its invisible, no light will be emitted. damn.

i guess youd need to tell vray to make the geometry transparent to gi rays hitting the back of the faces. that way rays coming from the cieling would pass through and hit lit geometry.

[super gnu]

-a 100% refractive, ior1 vraymtl on the back of a 2sided seems to work its only taken me years to figure that out. no idea of the speed penalty or if theres a more elegant way..

[Deflaminis]

That's.... brilliant.