Change light smoothing factor in lightweight renderpipeline to match lightmapper

com.unity.render-pipelines.lightweight/LWRP/Passes/SetupLightweightConstanstPass.cs

             if (lightData.lightType != LightType.Directional)
             {
                 // Light attenuation in lightweight matches the unity vanilla one.
-                // attenuation = 1.0 / 1.0 + distanceToLightSqr * quadraticAttenuation
-                // then a smooth factor is applied to linearly fade attenuation to light range
-                // the attenuation smooth factor starts having effect at 80% of light range
+                // attenuation = 1.0 / distanceToLightSqr
+                // We offer two different smoothing factors.
+                // The smoothing factors make sure that the light intensity is zero at the light range limit.
+                // The first smoothing factor is a linear fade starting at 80 % of the light range.
+
+                // The other smoothing factor matches the one used in the Unity lightmapper but is slower than the linear one.
+                // smoothFactor = (1.0 - saturate((distanceSqr * 1.0 / lightrangeSqr)^2))^2
-                lightAttenuation.x = oneOverFadeRangeSqr;
+                float oneOverLightRangeSqr = 1.0f / Mathf.Max(0.0001f, lightData.range * lightData.range);
+                lightAttenuation.x = SystemInfo.deviceType == DeviceType.Handheld ? oneOverFadeRangeSqr : oneOverLightRangeSqr;
                 lightAttenuation.y = lightRangeSqrOverFadeRangeSqr;
                 subtractiveMixedLighting = 1.0f;
             }

com.unity.render-pipelines.lightweight/LWRP/ShaderLibrary/Lighting.hlsl

     // for directional lights attenuation will be 1
     half lightAtten = 1.0h / distanceSqr;
 
+#if defined(SHADER_HINT_NICE_QUALITY)
+    // Use the smoothing factor also used in the Unity lightmapper.
+    half factor = distanceSqr * distanceAttenuation.x;
+    half smoothFactor = saturate(1.0h - factor * factor);
+    smoothFactor = smoothFactor * smoothFactor;
+#else
     // We need to smoothly fade attenuation to light range. We start fading linearly at 80% of light range
     // Therefore:
     // fadeDistance = (0.8 * 0.8 * lightRangeSq)
     // distanceSqr *        distanceAttenuation.y            +             distanceAttenuation.z
     half smoothFactor = saturate(distanceSqr * distanceAttenuation.x + distanceAttenuation.y);
+#endif
+
     return lightAtten * smoothFactor;
 }