Full invisible area light

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marcatore
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Full invisible area light

Post by marcatore »

HI,
I've read some messages on LuxCore Discord server to get the area lights invisible in terms of direct visibility and in terms of shadows.
Tipical situation is an area light near a ceiling.
I've tried to setup the light like suggested but it seems that some occlusion still existing and it reveals the area light shape.
I'm attaching a simple scene.
The scene contains 2 area lights. One visible and the other one invisible (the right one looking through the camera).
Is it possible to make the area light completely invisible? Just an "invisible" emitter?
I'd like to still use the MIS so opacity on a mesh light is not the best solution.

Thanks in advance
InvisibleAreaLight.zip
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B.Y.O.B.
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Re: Full invisible area light

Post by B.Y.O.B. »

To give a bit of context, what we have here is a meshlight which is invisible to the camera and has a white shadow color. Despite that, it still throws a slight shadow on the wall.

My response on discord was:
@marcatore It looks like the shadow color is not considered for global illumination rays.
When I change the ground plane to black matte, the shadow disappears. I think it comes from the fact that the whole wall is lit up slightly by indirect light from the ground, but this indirect light does not respect the shadow color and is blocked by the area light.
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Re: Full invisible area light

Post by marcatore »

Thank you for adding details.

let's see for the Dade's reply
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Re: Full invisible area light

Post by Dade »

I should have fixed this problem.
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Re: Full invisible area light

Post by marcatore »

Is it correct that the reflection of the "invisible" light is weaker than the visible one?

I'm doing some tests...it seems that also the direct light is weaker.
I'll post some images.
Last edited by marcatore on Thu Jul 02, 2020 2:06 pm, edited 1 time in total.
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Re: Full invisible area light

Post by B.Y.O.B. »

It looks like it is now partly invisible in glossy reflections and completely invisible in specular reflections.
From left to right: meshlight completely visible, meshlight invisible to camera and shadow color white, meshlight opacity = 0
At least it doesn't create noise like the meshlight with opacity = 0.
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marcatore
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Re: Full invisible area light

Post by marcatore »

I've test the invisible light with direct light. It seems that it emit less light.
I've attached a PSD with the 2 images that show the lighting difference.
invisibleLight_difference.zip
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Re: Full invisible area light

Post by Dade »

B.Y.O.B. wrote: Thu Jul 02, 2020 2:06 pm It looks like it is now partly invisible in glossy reflections and completely invisible in specular reflections.
From left to right: meshlight completely visible, meshlight invisible to camera and shadow color white, meshlight opacity = 0
At least it doesn't create noise like the meshlight with opacity = 0.
I have fixed that problem too. But note: the highlights, on the floor plane, aren't going to be exactly the same due to the indirect light received by the back plane, etc.

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Re: Full invisible area light

Post by marcatore »

Well..that it's more "correct" than before where the reflection was darker.
As soon as I can I'll test also the direct light. Or do you already test it? It's now the same?
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Re: Full invisible area light

Post by B.Y.O.B. »

Awesome!
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