You can place as many lights as needed, so there is no limit as too how many lights can be used to render. Obviously, performance is the biggest limiting factor and shadows is one of the biggest. Lights that don't cast shadows will run much quicker.
Also, with point lights and spots. The smaller the light, the faster it will run
Skyline Game Engine - Lead Dev. Please provide as much info as possible when asking for help.
Specs: OS: Win 10 64bit, CPU: Intel i7 4770 3.4ghz x 4 core(8 threads), GPU: Nvidia GTX 1060 6GB, Ram: 16gig DDR3, Windows on 250gb Samsung Evo 860