Explainer: https://github.com/immersive-web/lighting-estimation/blob/master/lighting-estimation-explainer.md

Spec: https://www.w3.org/TR/webxr-lighting-estimation-1/ (Editors' Draft)

This is the repository for the WebXR lighting estimation API, which provides XR sessions (primarily AR) with information about the current environment lighting so that cirtual objects can be rendered more realistically.

The features was initially proposed in this issue, though that proposal no longer matches the current API shape.