Wrong light emission direction with mirrored objects and VrayLightMtl?

[Alex_M]

I've been adjusting some lights when I found something strange. If you mirror an object which you have a VrayLightMtl applied on, the light continues to be emitted in the same direction. This doesn't happen with native vray light objects such as Vray Plane Light.

Try this:

1. Create a plane in the center of the scene and apply a simple grey material on it. Clone it and and place it some distance above the first one.
2. Create another, smaller plane between the 2 you already created and apply a VrayLightMtl material (make sure to turn on the option "Direct illumination" in this material).
3. Do a test render. The light shines upwards as expected.
4. Now mirror the light along the Z axis by using the Mirror tool in Main Toolbar of Max to make the small plane can cast light downwards.

The light continues to shine upwards even thought the object faces the opposite direction. You can check the direction the polys are facing by turning on "Backface Cull" in object properties of the small plane.





I found 2 workarounds - you can flip the object with a modifier (Mirror or Normals); you can also go into the polygon sub-object level and flip the normals of all polygons from there.

[TutanMark]

Should be another thread but it's too similar to create another...

To me It happens with mirrored Vraylights mesh objects as well.

[chaosseed]

This is another way

Check option~

[Alex_M]

Thanks, this works too.