Description of `Specular Tint` may be not clear enough

Documentation
1

Principled BSDF — Blender Manual says “Tints the facing specular reflection using the base color, while glancing reflection remains white.” ​But I cannot figure out the meaning of “facing specular reflection” and “glancing reflection”. Googling them didn’t give me any valid information, either.

Does “facing specular reflection” and “glancing reflection” means specular reflection that is reflected on the surface and diffuse color respectively ?
I have consult the source code of the principled BSDF shader but I am not pretty sure about the above idea.

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The different types of reflections are based on the angle at which you observe a surface. I don’t know how to properly describe them, so hopefully this image helps?

Different reflections
Different reflections914×834 62.5 KB

Take note of the face that I am looking at each face at different angles resulting in the different types of reflections.

Could the manual be updated to better explain things? Probably. But I don’t really know how to describe it so I will leave this task to someone else?

3

Thanks for your description. It is clear and intuitive.

To my knowledge, it is the frensel equation (rather than some feature of specular tint itself) that makes the right side surface of the cube whiter.

So will “Tints the specular reflection using the base color." plus a note that says something like “The ratio of specular reflection increase as the angle between light and the surface get smaller, so you will likely get a whiter reflection” be a better description?

Reference: