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For some reason, LightPath node doesn't work expectedly. When I plug in 'Is Diffuse Ray' output, I want to exclude all Diffuse rays but they stay. It works for Glossy ray and Camera ray, but why don't work for diffuse rays enter image description here enter image description here enter image description here

Here I have added more explanation for my question above

For Glossy shader, all work exactly how expected: for Cycles engine and HDRI background I can exclude Glossy surfaces from the scene (make a mask) enter image description here

But for Diffuse shader, when I use Cycle engine and HDRI I can exclude diffuse surfaces, for some reason, it doesn't work how it works for Glossy shader shown above enter image description here But when I try to use a flat colour background for Cycles, It becomes possible to exclude diffuse surfaces enter image description here or with HDRI but switch to Eevee it also works well enter image description here Okay, in the end, my simple question is why when I am using HDRI background and Cycle I can exclude Diffuse surfaces how it works well for Glossy surfaces for instance

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Using a Mix Shader node and 2 background nodes will give you better results and more flexibility than multiplying the strength of the entire world. you can also sorta "mask" it out and add whatever youd like on the 2nd background node and show one thing in the sky but for diffuse light bounces to react to another thing.

enter image description here but if you absolutely need to use the node's strength, then doing it without any sort of multiply works, if u need to multiply it, then add a multiply node and/or an invert node to change the background's strength, with shouldnt be a problem with my method since the strength socket is available

EDIT: with what u said in comments, that would need to be done in the compositing of the scene. you would need to enable diffuse layers for indirect diffuse, then use that as a mask/factor for the other ndoes enter image description here

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this will take all light bounces coming from diffuse surfaces to the camera and use them as a factor, take note this will also affect other diffuse indirect bounces though. or, you can play around with materials and use the light path node on them and experiment a little

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  • $\begingroup$ Hello, here is a misunderstanding, probably it is my poor explanation. My goal is to make a mask for all Diffuse objects for a scene which are lighted by background. I don't want to influence the background. Below I have added more explanation $\endgroup$
    – Vitalii Sadovshikov
    Commented Jun 23, 2020 at 6:52

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