Only point lights affect indirect lighting on RTGI much less than other types of lights.
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Indirect lighting of baked lightmaps look much stronger than RTGI.
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Apparently, it's because only point lights are divided by 4*PI in SetupLightParameters of Engine\Source\Runtime\Renderer\Private\RayTracing\RayTracingGlobalIllumination.cpp

		case LightType_Point:
			LightParameters->Type[LightParameters->Count] = 1;
			LightParameters->Position[LightParameters->Count] = LightShaderParameters.Position;
			// #dxr_todo: UE-72556 define these differences from Lit..
			LightParameters->Color[LightParameters->Count] = LightShaderParameters.Color / (4.0 * PI);
			float SourceRadius = 0.0; // LightShaderParameters.SourceRadius causes too much noise for little pay off at this time
			LightParameters->Dimensions[LightParameters->Count] = FVector(0.0, 0.0, SourceRadius);
			LightParameters->Attenuation[LightParameters->Count] = 1.0 / LightShaderParameters.InvRadius;

I removed the 4*PI then it fixed this issue and indirect lighting from a point light on RTGI looks more similar to baked lighting. (Shelved CL: 14023328 on 4.25plus)
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Steps to Reproduce
  1. Open the attached project
  2. You can see the point light does't affect indirect lighting well
  3. Build lighting, you can see the baked lightmaps have indirect lighting.

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ComponentRendering - Ray Tracing
Affects Versions4.254.25plus
Target Fix4.26
Fix Commit14466725
CreatedAug 4, 2020
ResolvedOct 13, 2020
UpdatedOct 23, 2020