UE4.25 RenderDeferredLighting 18% higher than 4.24

Hey folks,

I am seeing a noticeably higher RenderDeferredLighting cost switching from 4.24 to 4.25 of around 1.9 ms on 4.24 up to 4 ms on 4.25. I have tested a couple frames in my level to make sure and it appears to be consistent and results in a roughly 18% performance hit in my level.

On 4.24

On 4.25

Additionally deleting my sky light, my skysphere and my directional light does not reduce the cost, however disabling deferred lighting through the flags does reduce the cost down to 0. Starting with an empty level incurs 0 deferred lighting time, however starting with the default level and deleting everything still results in <0 deferred lighting time.

To conclude I’m very confused, and would appreciate some guidance on this one.


If removing those lights made no change, it’s likely a profiling artifact. There is something about GPU driver bubbles or something that makes the time get assigned to the wrong actions.

Did your full frame time increase by the same amount?

Yes the full frame time and the frame rate itself was affected

For anyone following this thread, disabling SSGI under my Rendering settings on 4.25 reduced my RenderDeferredLighting cost MASSIVELY. Turning off SSGI on 4.25 resulted in about 27% less GPU time.