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Why is there a dedicated Emission shader when the Principled BSDF has an emission slot? If I plugged the same image texture both into the color of an Emission shader and the emission color of a Principled BSDF, would I not get the same result? (Assuming the emission strength was the same)

I understand that, in versions of Blender before the BSDF, you would have to mix multiple types of shaders to get the desired result. Now that we have the Principled BSDF, (which also calculates Fresnel and energy conservation) I figured the other shader nodes would no longer be needed. After reading this question, my suspicions seemed to be confirmed, but I could still be missing something.

I was thinking that the "simple" shaders are more resource-efficient than the full BSDF, since they're doing less computationally. Maybe this is why they are still in Blender?

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    $\begingroup$ The Principled BSDF is like a mix of nodes so if you plug an image into the Emission it won't give the same result as a simple Emission, it will be mixed with the inherent Diffuse, at least from what i've tried $\endgroup$
    – moonboots
    Feb 12 at 22:42
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    $\begingroup$ The Emission part of the Principled BSDF can be used to only give for example a bit of emission additionally to other surface shading provided by the Principled BSDF, also this makes it easy to only have certain parts of a mesh emissive by using masking, for example a building texture where you give some windows light by plugging a mask into the Emssion Strength. But sometimes you don't need all that and a simple Emission shader is sufficient - and it existed in Blender before the Principled BSDF. $\endgroup$ Feb 13 at 12:15

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PrincipledBSDF is meant to be convenient to use and to unify workflows across different software.

Principled BSDF

The Principled BSDF that combines multiple layers into a single easy to use node. It can model a wide variety of materials.

It is based on the OpenPBR Surface shading model, and provides parameters compatible with similar PBR shaders found in other software, such as the Disney and Standard Surface models. Image textures painted or baked from software like Substance Painter may be directly linked to the corresponding input in this shader.

https://docs.blender.org/manual/en/latest/render/shader_nodes/shader/principled.html

It is meant to be familiar and compatible. This does not mean it is meant for everything and is best at everything in all circumstances(although it's pretty good for most cases). PBR is only one workflow and it is not for completely everything. Some situations require screen referred workflows for various graphics(as opposed to scene referred workflow that is so called PBR) or NPR(non-photorealistic rendering). It is easier to construct complex shaders out of smaller basic building blocks and it's also more efficient to use only what you need in those cases.

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  • $\begingroup$ More efficient, in terms of render speed, or in ease of use? $\endgroup$ Feb 12 at 22:58
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    $\begingroup$ It can be both. It's not general and depends on very specific circumstances. I am not saying PrincipledBSDF is not efficient. It is. But there are so many different situations. $\endgroup$ Feb 12 at 23:00
  • $\begingroup$ Ok, I gotcha ya. Thanks! $\endgroup$ Feb 12 at 23:03

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