Moved area light convertion code to LightUtils

com.unity.render-pipelines.high-definition/HDRP/Editor/Lighting/HDLightEditor.cs

         enum DirectionalLightUnit
         {
             Lux = LightUnit.Lux,
-            Ev = LightUnit.Ev,
         }
 
         enum AreaLightUnit
         {
             Lumen = LightUnit.Lumen,
             Candela = LightUnit.Candela,
-            Ev = LightUnit.Ev,
         }
 
         const float k_MinAreaWidth = 0.01f; // Provide a small size of 1cm for line light
 
             // For area lights
             if (oldLightUnit == LightUnit.Lumen && newLightUnit == LightUnit.Luminance)
-            {
-                if (m_LightShape == LightShape.Rectangle)
-                    intensity = LightUtils.ConvertRectLightLumenToLuminance(intensity, m_AdditionalLightData.shapeWidth.floatValue, m_AdditionalLightData.shapeHeight.floatValue);
-                else if (m_LightShape == LightShape.Line)
-                    intensity = LightUtils.CalculateLineLightLumenToLuminance(intensity, m_AdditionalLightData.shapeWidth.floatValue);
-            }
+                intensity = LightUtils.ConvertAreaLightLumenToLuminance((LightTypeExtent)m_AdditionalLightData.lightTypeExtent.enumValueIndex, intensity, m_AdditionalLightData.shapeWidth.floatValue, m_AdditionalLightData.shapeHeight.floatValue);
-            {
-                if (m_LightShape == LightShape.Rectangle)
-                    intensity = LightUtils.ConvertRectLightLuminanceToLumen(intensity, m_AdditionalLightData.shapeWidth.floatValue, m_AdditionalLightData.shapeHeight.floatValue);
-                else if (m_LightShape == LightShape.Line)
-                    intensity = LightUtils.CalculateLineLightLuminanceToLumen(intensity, m_AdditionalLightData.shapeWidth.floatValue);
-            }
+                intensity = LightUtils.ConvertAreaLightLuminanceToLumen((LightTypeExtent)m_AdditionalLightData.lightTypeExtent.enumValueIndex, intensity, m_AdditionalLightData.shapeWidth.floatValue, m_AdditionalLightData.shapeHeight.floatValue);
+            if (oldLightUnit == LightUnit.Luminance && newLightUnit == LightUnit.Ev)
+                intensity = LightUtils.ConvertLuminanceToEv(intensity);
+            if (oldLightUnit == LightUnit.Ev && newLightUnit == LightUnit.Luminance)
+                intensity = LightUtils.ConvertEvToLuminance(intensity);
+            if (oldLightUnit == LightUnit.Ev && newLightUnit == LightUnit.Lumen)
+                intensity = LightUtils.ConvertAreaLightEvToLumen((LightTypeExtent)m_AdditionalLightData.lightTypeExtent.enumValueIndex, intensity, m_AdditionalLightData.shapeWidth.floatValue, m_AdditionalLightData.shapeHeight.floatValue);
+            if (oldLightUnit == LightUnit.Lumen && newLightUnit == LightUnit.Ev)
+                intensity = LightUtils.ConvertAreaLightLumenToEv((LightTypeExtent)m_AdditionalLightData.lightTypeExtent.enumValueIndex, intensity, m_AdditionalLightData.shapeWidth.floatValue, m_AdditionalLightData.shapeHeight.floatValue);
 
             m_AdditionalLightData.intensity.floatValue = intensity;
         }

com.unity.render-pipelines.high-definition/HDRP/Lighting/Light/HDAdditionalLightData.cs

 
             if (lightUnit == LightUnit.Lumen)
             {
-                switch (lightTypeExtent)
-                {
-                    case LightTypeExtent.Punctual:
-                        SetLightIntensityPunctual(intensity);
-                        break;
-                    case LightTypeExtent.Line:
-                            m_Light.intensity = LightUtils.CalculateLineLightLumenToLuminance(intensity, shapeWidth);
-                        break;
-                    case LightTypeExtent.Rectangle:
-                        m_Light.intensity = LightUtils.ConvertRectLightLumenToLuminance(intensity, shapeWidth, shapeHeight);
-                        break;
-                }
+                if (lightTypeExtent == LightTypeExtent.Punctual)
+                    SetLightIntensityPunctual(intensity);
+                else
+                    m_Light.intensity = LightUtils.ConvertAreaLightLumenToLuminance(lightTypeExtent, intensity, shapeWidth, shapeHeight);
+            }
+            else if (lightUnit == LightUnit.Ev)
+            {
+                m_Light.intensity = LightUtils.ConvertEvToLuminance(intensity);
             }
             else
                 m_Light.intensity = intensity;

com.unity.render-pipelines.high-definition/HDRP/Lighting/LightUtils.cs

             return intensity * ((width * height) * Mathf.PI);
         }
 
+        public static float ConvertEvToLuminance(float ev)
+        {
+            return Mathf.Pow(2, ev - 3);
+        }
+
+        public static float ConvertLuminanceToEv(float luminance)
+        {
+            const float k = 12.5f;
+
+            return (float)Math.Log((luminance * 100f) / k, 2);
+        }
+
+        public static float ConvertAreaLightLumenToLuminance(LightTypeExtent areaLightType, float lumen, float width, float height = 0)
+        {
+            switch (areaLightType)
+            {
+                case LightTypeExtent.Line:
+                    return LightUtils.CalculateLineLightLumenToLuminance(lumen, width);
+                case LightTypeExtent.Rectangle:
+                    return LightUtils.ConvertRectLightLumenToLuminance(lumen, width, height);
+            }
+            return lumen;
+        }
+
+        public static float ConvertAreaLightLuminanceToLumen(LightTypeExtent areaLightType, float luminance, float width, float height = 0)
+        {
+            switch (areaLightType)
+            {
+                case LightTypeExtent.Line:
+                    return LightUtils.CalculateLineLightLuminanceToLumen(luminance, width);
+                case LightTypeExtent.Rectangle:
+                    return LightUtils.ConvertRectLightLuminanceToLumen(luminance, width, height);
+            }
+            return luminance;
+        }
+
+        public static float ConvertAreaLightLumenToEv(LightTypeExtent areaLightType, float lumen, float width, float height)
+        {
+            float luminance = ConvertAreaLightLumenToLuminance(areaLightType, lumen, width, height);
+
+            return ConvertLuminanceToEv(luminance);
+        }
+
+        public static float ConvertAreaLightEvToLumen(LightTypeExtent areaLightType, float ev, float width, float height)
+        {
+            float luminance = ConvertEvToLuminance(ev);
+
+            return ConvertAreaLightLuminanceToLumen(areaLightType, luminance, width, height);
+        }
+
         // convert intensity (lumen) to nits
         public static float CalculateLineLightLumenToLuminance(float intensity, float lineWidth)
         {