Fixed comment and typo about line light function/calculation

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/HDRenderPipelineMenuItems.cs

                 }
                 else if (add.lightTypeExtent == LightTypeExtent.Line)
                 {
-                    add.areaIntensity = l.intensity / LightUtils.CalculateLineLightArea(1.0f, add.shapeWidth);
+                    add.areaIntensity = l.intensity / LightUtils.CalculateLineLightIntensity(1.0f, add.shapeWidth);
                 }
             }
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Lighting/HDLightEditor.cs

                     break;
 
                 case LightShape.Line:
-                    settings.intensity.floatValue = LightUtils.CalculateLineLightArea(m_AdditionalLightData.areaIntensity.floatValue, m_AdditionalLightData.shapeWidth.floatValue);
+                    settings.intensity.floatValue = LightUtils.CalculateLineLightIntensity(m_AdditionalLightData.areaIntensity.floatValue, m_AdditionalLightData.shapeWidth.floatValue);
                     break;
             }
         }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Light/HDAdditionalLightData.cs

             }
             else if (lightTypeExtent == LightTypeExtent.Line)
             {
-                light.intensity = LightUtils.CalculateLineLightArea(areaIntensity, shapeWidth);
+                light.intensity = LightUtils.CalculateLineLightIntensity(areaIntensity, shapeWidth);
             }
         }
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightUtils.cs

         }
 
         // convert intensity (lumen) to nits
-        public static float CalculateLineLightArea(float intensity, float lineWidth)
+        public static float CalculateLineLightIntensity(float intensity, float lineWidth)
-            // The area of a cylinder is this:
-            // float lineRadius = 0.01f; // 1cm
-            //return intensity / (2.0f * Mathf.PI * lineRadius * lineWidth * Mathf.PI);
-            // But with our current line light algorithm we get an insane gap in intensity
-            // following formula (fully empirical) give a better match to a rect light of 1cm of width.
-            // It is basically point light intensity / line width.
+            // Line lights in the shader expect intensity (W / sr).
+            // In the UI, we specify luminous flux(power) in lumens.
+            // First, it needs to be converted to radiometric units(radiant flux, W).
+            // Then we must recall how to compute power from intensity for a line light:
+            // power = Integral{length, Integral{sphere, intensity}}.
+            // For an isotropic line light, intensity is constant, so
+            // power = length * (4 * Pi) * intensity,
+            // intensity = power / (length * (4 * Pi)).
             return intensity / (4.0f * Mathf.PI * lineWidth);
         }
     }