Building lighting and performance

Since I am relatively new to all of this, I wanted to know how Unreal Editor/Engine uses the resources it has. For instance, does the engine just know how much juice the video card has and uses that over CPU cycles when applicable?

For instance currently I am building lighting on a scene and it is just red-lining the CPU but am not sure if the GPU and its resources are being tapped.

Is there a way to know this or settings somewhere to tell how much to use or not use?

Thanks.

Building lighting uses the CPU mostly (export uses GPU). All of your cores minus 2 are used for the lighting rebuild. The value is in BaseLightmass.ini - NumUnusedLightmassThreads. If you have 4 cores or less it will do Numcores-1 instead.

For rendering, the engine / editor just updates as fast as it can. There might be a framerate cap, not sure.

Thank you.