The read-only primaryLightDirection property of the XRLightEstimate interface returns a DOMPointReadOnly representing the direction to the primary light source from the probeSpace of an XRLightProbe.

A DOMPointReadOnly object. If no estimated values from the user's environment are available, the point will be { x: 0.0, y: 1.0, z: 0.0, w: 0.0 }, representing a light shining straight down from above.

Within an XRFrame loop, you can use the primaryLightDirection and primaryLightIntensity properties to render shadows based on the most prominent light source, for example.

const lightProbe = await xrSession.requestLightProbe();

// frame loop
function onXRFrame(time, xrFrame) {
  let lightEstimate = xrFrame.getLightEstimate(lightProbe);

  // Render lights ...

  // Available properties
  lightEstimate.primaryLightDirection;
  lightEstimate.primaryLightIntensity;
}

• XRLightEstimate.primaryLightIntensity
• XRLightProbe.probeSpace