Let me correct you there, you said illusion that put so many light in the game.
F5 was part of a mods that called Graphics Plugin, it was created by a modder name Hanmen.
The lights it self was setting default by Hanmen like that, according to his PC spec. It was not illusion fault
the first time you play HS2 using this Graphics Plugin, you need to set up the F5 all setting not just the lights.
If you get decrease FPS, you need to set up all the setting in F5. Sometime even you need to disable the shadow in setting if your PC is not strong enough.
this is the link of Hanmen Graphics Plugin:
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