strange behavior of quad light

[marchermitte]

Hello!
I'm puzzled , probably doing something wrong but It seems to me that (once the opacity is set to 0) , the lights shouldn't interact with the surrounding geometry, exept to spread luminosity around. (I get ambiant occlusion casted from the lights on the walls It's close to in direct lighting, both in ambiant occlusion and diffuse mode with ambiant occlusion)
Plus the behavior of the light doesn't seem very natural to me... In this picture, I added a quad light around the lampshade, made It 0% opaque and I find wierd the way It shows against the wall... am I missing something?

Thank you!

[juanjgon]

Are you using the dirt node in the wall material?

-Juanjo

[juanjgon]

Nope, this is not the problem. I am testing your issue and it is true, the light is a shape that can't be hidden from diffuse rays, so it is always visible for AO or diffuse indirect lighting.

Sorry, currently you only can hide a shape for the camera or shadow rays, but not for the other rays, so the lights shapes are always visible for the global illumination or AO (and also of course for the dirt node).

-Juanjo

[marchermitte]

Thank you for your reply Juanjgon.
Well, that sucks... how can I solve this case, having the light that close to the wall and acting naturaly... no ambiant occlusion at all I guess, or using pmc? (meaning longer render time also) Or render a region around the emiter without the ambiant occlusion in this area, and then comp the results.
Any idea if that could be "corrected" in next releases? I guess It's more an Octane issue than an Octane for Lightwave plugn issue but
It seems to me that a light shouldn't emit luminosity AND be seen by ambiant occlusion or shadow rays...

[juanjgon]

Yes, I agree that in the future Octane should support more ray visibility options to avoid this issues (now as I say before you only can hide a mesh for the camera and shadow rays, you can't hide the meshes for AO or indirect diffuse or specular rays).

Anyway I think that your best chance is to try to light the scene physically, not using fake lights ... why do you need this light in this location?, perhaps you could use the lamp light to illuminate this area. The root problem is that Octane is a physically based renderer that only has real mesh lights, it is not designed to build "fake" lighting setups, and it doesn't have some options needed to work with fake lights (like as you can see for example a full unseen by rays option for meshes, or virtual light sources without a mesh).

Also anyway I am testing a very simple scene with a cube light and I don't get this artifact in the image ... perhaps you could also use a modeled ball with an emission material as light source, perhaps this could avoid the shadows cross shape in the wall.

If you want to send the scene to me I could test it here to see what is the best way to light it.

-Juanjo

[marchermitte]

ok, this is strange. I cut the room from the whole project (the complete scene is heavy) and set up only the lamp with the light (same position, light, etc) and the render doesn't show the artifact (you can see It at the beginning pf the IPR but not any more after a few seconds)
I should send you the complete scene, I'm trying to find the cause of those 2 different behaviors without success...

[MrFurious]

Nope, this is not the problem. I am testing your issue and it is true, the light is a shape that can't be hidden from diffuse rays, so it is always visible for AO or diffuse indirect lighting.

Sorry, currently you only can hide a shape for the camera or shadow rays, but not for the other rays, so the lights shapes are always visible for the global illumination or AO (and also of course for the dirt node).

-Juanjo

...and Reflections (sighs..) this is long overdue cmon otoy