UnityARAmbient.cs

using System.Runtime.InteropServices;
using UnityEngine.XR.iOS;

namespace UnityEngine.XR.iOS
{
    public class UnityARAmbient : MonoBehaviour
    {

        private Light l;

        public void Start()
        {
            l = GetComponent<Light>();
			UnityARSessionNativeInterface.ARFrameUpdatedEvent += UpdateLightEstimation;
        }

		void UpdateLightEstimation(UnityARCamera camera)
		{
			if (camera.lightData.arLightingType == LightDataType.LightEstimate) {
				// Convert ARKit intensity to Unity intensity
				// ARKit ambient intensity ranges 0-2000
				// Unity ambient intensity ranges 0-8 (for over-bright lights)
				float newai = camera.lightData.arLightEstimate.ambientIntensity;
				l.intensity = newai / 1000.0f;

				//Unity Light has functionality to filter the light color to correct temperature
				//https://docs.unity3d.com/ScriptReference/Light-colorTemperature.html
				l.colorTemperature = camera.lightData.arLightEstimate.ambientColorTemperature;
			}
		}

		void OnDestroy() {
			UnityARSessionNativeInterface.ARFrameUpdatedEvent -= UpdateLightEstimation;
		}
    }
}