VRay light made 'Invisible' behind clear object removes refraction.

[RobH2]

I have an object with a glass material in VRay. All photographers know to light glass from behind. When I put a V-Ray Plane light behind an object with a glass material the refraction looks fantastic.

But, I can see the white shape of the light behind and I want my object on a very dark background. When I make the light 'Invisible' (like we always do when we don't  actually want to see the physical light object) the refracted light coming through goes away. 

What I've always loved about 3d lighting is the ability to do things with lights that you can't in the studio, most importantly, being able to hide the light object and still have it cast rays.

Is there a way to have a light behind a glass object and hide it and still have the light come through?

I've included two renders. On the left is the light behind and the nice refraction. On the right I've made the light 'Invisible' and background looks like I need it to but the refracted light is gone. The reflection under the object is there so I know the light is on but the refraction is gone.

I know I could render an alpha and composite to remove the light behind the object but I'd rather just have it be invisible and still function properly.

[cdecker86]

Try going into the light settings, and uncheck "affect reflections".

I am having a similar issue.  I turned off that setting, and now the light does not show up in the mirror, which is what I wanted.  But now it does not reflect properly on metals, like brass candlesticks.

- Cindy -

[RobH2]

Hi Cindy,

So, to solve it you have to put a VRayLightMtl on the plane behind the object that you want refraction in. What you give up is the ability to 'exclude' objects. Make sure you turn on 'Direct Illumination' in the material. Also, make sure the plane is invisible to the camera (turn off 'visible to camera') in the 'Object Properties.'