…Yeah…don’t make that many lights yet, please All of those lights are completely dynamic, and right now, we’re using a ‘forward’ renderer to draw lights, which basically just ‘adds’ lighting to the scene by figuring out what kind of geometry is affected by the light, and drawing that lit geometry. This means that if you have 100 lights, we are figuring out what geometry is lit by that light, and then drawing that geometry–100 times. Per frame. This is not cheap
In the near-ish future: for players with older machines, they’ll have to make due with the forward renderer, because that’s fast (for small numbers of lights) and not use many lights (we’ll probably do something to ensure we just don’t draw many lights at once; not sure yet how this’ll work). For the higher end (such as your rig), we’ll introduce a ‘deferred’ rendering solution that is a lot more efficient with large numbers of lights (in the low hundreds).
(In the deeper future, I fantasize about writing a ‘tiling-based lighting engine’, which, for the top-end, can handle tens-of-thousands of dynamic lights in a scene…)