Hi ERuts,
Dynamic Shadow casting lights are the most expensive and this largely depends on the number of shadow casting meshes in the scene along with number of dynamic lights in the scene.
Stationary Point and Spot lights are meant to be used to bake static lighting for all static objects in the scene and provide dynamic lighting for movable objects and characters. When more than 4 of these overlap they will show a red X over the light and will default to Dynamic lights. This can be the performance overhead you’re experiencing.
When these lights are set to not cast shadows, since they are defaulting to dynamic it is why you’re seeing performance jump back up.
The biggest thing to do when running into performance issues where you’re seeing a significant drop in frames is to use profiling to narrow down where this is happening.
These two pages should help explain how to do this:
To briefly answer your other questions.
Performance hits can happen with dynamic and static lighting. With static lighting, have extremely large Lightmap resolution can increase your texture memory footprint and cause performance issues. Using dynamic lighting will depend on the lights settings with radius, strength, how many objects are casting shadows, etc. When lighting large scenes, It’s best to understand what your target platform is, whether you’ll need dynamic or static lighting, lighting the scene appropriately and then profiling to see where the biggest hits are coming in. When you narrow down the performance hits you can then start to refine your scenes more to fit your system specs or the target system specs.
Thank you!
Tim