Ambient light brightes metal materials with high roughness

In the current dev version materials with a metalness of 1 get brighter through the ambient light. The rougher they are the stronger the efffect is.

Testscene

Sphere left side: metalness: 1, roughness: 0, Sphere right side: metalness: 1, roughness: 1 AmbientLight Intensity: 2

Expected (r107)

The ambient light intensity does not change the brightness of metal materials
jsfiddle master

Actual (dev)

The ambient light intensity changes the brightness of the smooth metal a bit and the brightness of the rough metal a lot.
jsfiddle dev

Three.js version

• Dev
• r107

Browser

• All of them

OS

• Windows

[sunag]

@WestLangley probably it is related with the clearcoat normal PR, these changes add others behavior related to the lights_physical_pars_fragment. I create a test to ensure if preserve-energy is the bug causing, bellow. I will have to look at this more calmly to find out the origin.

https://jsfiddle.net/zdyf196n/ https://github.com/sunag/three.js/tree/dev-bug-test1

[WestLangley]

@sunag

1. You are confusing diffuse reflectance and specular energy conservation. Metals do not reflect diffusely. The increased brightness you see in the babylon playground is specular energy.
2. Babylon has a different hemisphere-light model than three.js does – babylon’s has a specular hot-spot; three.js’ does not.
3. three.js ambient light has no specular component, either.