Low FPS when lighting needs rebuilding


Ive been working on a scene for a while and recently im noticing some really low fps (5-7fps) when the lighting needs rebuilding (red warning message) , normally its up around the 45-50fps. After I`ve rebuilt the lighting its fine. Any ideas
whats going on behind the scenes that could be causing it. No matter how many objects i hide from the scene the fps is really low until I do a build.
Its only just started happening but cant figure out what could be causing this issue.

I`m using Unreal 4.7.4 btw


Hi Paul,

When lighting needs to be rebuilt the scene is using Dynamic Lighting to give shadows for those objects that have not had lighting built yet. When you build lighting they are using their static baked lighting which can improve FPS. Dynamic Lighting when casting shadows is an expensive process and the results can depend on the number of objects in the view casting shadows and system specs.

Great thanks Tim, I wondered if it was that. What is odd is that even when I`m hiding from view almost all of my static objects in the scene its still very low fps. Should it not ignore dynamically lighting objects if theyre invisible?

Hi Again

Well have been struggling along with this, something doesnt seem right with my scene.ts a complex scene with some 2.5m tris and 114,000k current texture memory .but Im having to rebuild the lighting almost every time i do any changes otherwise its down to 5-8fps which is unusable. Even now when its not asking to rebuild of lighting, i hide everything apart from a few objects and put it into wireframe and im still only get 5-8 fps.
Now i`m not on a top end gpu (its a geforce gtx 465 on a i7 2600k, 16gb ram) but normally the scene is running with everything around 50fps. Then all of a sudden, i do some changes and its back slowing down. Surely hiding everything and put it into wireframe shouldnt get these results.

Any ideas? Thanks


ok now this is weird. I just finished writing the above post, went back to unreal, hid the statistics panel and the fps shoots upto 110fps for the above , from 5.86 which its been stuck on for 10-15mins.

well i`ve got around it by disabling real time rendering in the viewport, then everything is much faster.