So, i decided to try out what really cost in terms of performance when using lights, because on the internet we hear anything. I put 600 lights on a map and tryed to increase values to their maximum and here are the results in you’re interested, in terms of impact on FPS.
Intensity: No impact
Attenation radius: HUGE impact
Source radius: Very little impact
Soft source radius: No impact
Source lenght: No impact
Indirect intensity: No Impact
Volumetric scattering intensity: No impact
Cast shadows: HUGE impact.
Knowing this you should be able to tweak your lights more efficiently, however you can also try to go into Project Settings > Culling> Min Screen Radius for Lights and here, if you change default 0.03 to a higher value, you can cull lights that are too far away and sometimes useless, 0.08 helps a lot !
