Urgent! Mesh lights/VrayLight materials not casting light

[Alex_M]

Hi,

I've got a very urgent issue with a rendering that I have to deliver very soon. I've got furniture which I need to add LED strips to (in the plinth) and the only way to do it is by using mesh light or VrayLight material because the furniture is curvy/irregular shape so I can't use regular rectangular plane lights. The problem is that VrayLight material and Mesh lights cast almost no light even with very high intensities. Not only this but they render EXTREMELY noisy even when left to render for a very long time compared to regular plane lights which clear up in seconds. How can I make it work?

All Vray settings are at default and the normals are not flipped. Vray version is in the signature. Please check the image below. I'm about to hit the deadline so any help is appreciated.

Edit: I've scene the scene to support.

[NicoC]

Hello,

Did you check the mesh normals ?
Also, since you don't precise it, I guess you're using VRay Adv and not RT ?

[Alex_M]

Normals are not flipped. I'm using Adv.

[NicoC]

Hmmm crap ... I'm afraid I don't have more ideas

[Raven]

Have you tried with adaptive lighting turned off? Not sure if it could be the issue.

[NicoC]

Good idea, Raven.
Best would be to share a stripped down version of scene, so that others could test ...

[Alex_M]

Tried, no change. I might just render this light on a separate pass, crank up the multiplier to something like a 1000, use denoiser and deal with it in post.

[NicoC]

OK, the essential is that you found a workaround, thus allowing you to deliver. However, I'd be curious to get CG guys feedback for this kind of problem.
Maybe worth checking if updating to the latest VRay version solves your problem.

[Raven]

Can you save just the mesh light out, would like to take a look, as I have not come across a problem like this before.
To me, it must have something specific to do with this geometry.

[Alex_M]

Scene attached.

[Raven]

It looks like it has to do with face normal directions.
Take a look at the image. On your light, the bottom-most faces of you light are not pointing straight down.
I did a test recreating it from the spline of the chair base and adjusted the angle on the spline render settings so faces are pointing directly down.

[Alex_M]

Thanks for taking the time to troubleshoot it, Raven. I think this might be it! Really appreciated. It is indeed a lot better, I didn't even consider that the shape being round would affect the casting of light downwards. It's still really slow and noisy though even when left to render for a while. Maybe this is the nature of mesh lights?

[kosso_olli]

I have to use mesh lights a lot on car interiors for ambient lighting. It is not much slower then a regular light.