vray light blocking GI?

[andrewjohn81]

I have a cabinet, all white, and I'm looking into it with open doors. With no lights it looks pretty white.
If I have a large vray light, similar to what a photographer would use in a studio, that i was hoping to use to act like it was bouncing light into the fridge. I wanted to add only a little light so I changed the multiplier to .2

The problem is that when I have that object it's actually blocking light and it's much darker. Is there a way to fix that? I don't want to use geometry as a bounce card because it usually makes the scene splotchy and it's hard to know the GI reflectivity of an object. Let me know if you know the answer to that. I was use to Mental Ray in the past where reflectivity directly relates to the GI reflectivity and you can also multiply that number, but the default multiplier is 1. If anyone knows the correlation of GI reflection to reflectivity then let me know. I haven't found any link.

So is the vray light suppose to block GI? how do I get it to stop?

[sv]

can't say for sure without testing, but try making it invisible?

[andrewjohn81]

I should have mentioned that. It is invisible already.

[vlado]

You can use a VRayMtlOverride material where the material visible to the camera is transparent, and the GI material is a VRayLightMtl material (also transparent, but light-emitting as well).

Best regards,
Vlado

[andrewjohn81]

I'm not sure how the GI light is reflected from the vray light material though.

I'd like the light, in this case, to have some direction using the normals of the plane. Does vray light material do that?

Also, I don't really want this object to cast shadows. How can vray light mat deal with that?

[Clifton Santiago]

So if I am understanding your first post, you want both the GI from the room, and also the vray light to illuminate the inside of the cabinet? You could forgo the vray light and just increase GI received of the geometry inside the cabinet.

Or, I would try pulling the vray light back so it doesn't block the ambient light and increase the multiplier. Also, include only the inside of the cabinet in the light settings.

Alternatively you could check the skylight portal option to force more GI into the cabinet...

If you want it to cast no shadows, which will make it look flat and fake, just use a max directional light with no shadows with a rectangular hotspot/falloff beam.

[andrewjohn81]

Thanks Clifton. For one thing my understanding of GI object settings was a little backwards. Once I thought about it more it made sense.
I changed the recieve number to 1.3 or something like that and it definitely brightened up while still having a good amount of contrast to describe the shape.

This allowed me to just scrap the light completely so I'm not going to mess around with that anymore.

Re casting shadows looking fake: I'm not impressed with how vray casts shadows for transparent objects, so if a light is only really looking through tranparent objects and thin objects then we often just eliminate the shadows all together and just use the light more to add some light to get a subtle gradation to describe the shape. Usually my clients like some different value across flat shapes to make them seem more interesting. We sometimes accomplish that with a large light at an angle.

[Clifton Santiago]

Okay good. Have you tried checking the "affect shadows" option in your glass materials? The shadows should look correct on transparent objects with that checked.

[andrewjohn81]

that helps, but they don't look correct.
All the time I end up having to do a clear plastic piece on top of a solid plastic piece. The clear piece can be 100% transparent and simply checking that box still makes it much too dark behind the plastic.
I have to change the object properties to not cast/receive shadows as well as uncheck visible to GI in the vray properties.

[Clifton Santiago]

Okay, I don't know then. I have no such problems. If your material is set up right, the shadows should look pretty photo-real. You could enable caustics for more realistic shadows, but it will slow things down.