Added comments

com.unity.render-pipelines.high-definition/HDRP/Editor/Sky/HDRISky/HDRISkyEditor.cs

             readBackTexture = null;
         }
 
+        // Compute the lux value in the upper hemisphere of the HDRI skybox
-            // GPU texture readback
+
             float omegaP = (Mathf.PI * 4) / (6.0f * hdri.width * hdri.width);
             m_IntegrateHDRISkyMaterial.SetTexture(HDShaderIDs._Cubemap, hdri);
             m_IntegrateHDRISkyMaterial.SetFloat(HDShaderIDs._InvOmegaP, 1.0f / omegaP);
+            // Copy the rendertexture containing the lux value inside a Texture2D
+            // And then the value inside this texture
             Color hdriIntensity = readBackTexture.GetPixel(0, 0);
             m_UpperHemisphereLuxValue.value.floatValue = hdriIntensity.r;
         }
                 PropertyField(m_IntensityMode);
             }
             if (EditorGUI.EndChangeCheck())
+            {
+            }
 
             if (m_IntensityMode.value.enumValueIndex == (int)SkyIntensityMode.Lux)
             {

com.unity.render-pipelines.high-definition/HDRP/Sky/HDRISky/HDRISky.shader

     TEXTURECUBE(_Cubemap);
     SAMPLER(sampler_Cubemap);
 
-    float4   _SkyParam; // x exposure, y multiplier, z rotation, w lux
+    float4   _SkyParam; // x exposure, y multiplier, z rotation
     float4x4 _PixelCoordToViewDirWS; // Actually just 3x3, but Unity can only set 4x4
 
     struct Attributes

com.unity.render-pipelines.high-definition/HDRP/Sky/HDRISky/IntegrateHDRISky.shader

             #pragma fragment Frag
             #pragma target 4.5
             #pragma only_renderers d3d11 ps4 xboxone vulkan metal switch
-#pragma enable_d3d11_debug_symbols
 
             #include "CoreRP/ShaderLibrary/Common.hlsl"
             #include "CoreRP/ShaderLibrary/Color.hlsl"