Note that installing the mod alone is not enough if you want to turn down the lighting. It gives you an option, but that option starts out at the game's default.
Press Ctrl+Shift+Backspace to bring up the control panel, then under the "NieR: Automata" subheading, lower the Global Illumination Quality setting. Turning it off is not recommended unless you're struggling to run the game at any resolution, since that causes some areas (e.g. around the access point in the park) to look really weird.
If you can't bring up the control panel, then most likely something went wrong during installation or you're running into an issue with third-party software. Many programs that display an overlay (Fraps, RTSS, Discord (when using the overlay)...) can cause issues.
If you're still having problems without such programs, try uninstalling the mod, removing the "My Mods" folder (note this also contains configuration for Kaldaien's other mods, if you're using any), removing anything left in your game folder except the standard "_CommonRedist", " data", "NierAutomata.exe", " steam_api64.dll", then reinstalling the mod. If automatic installation (via SKIM64) doesn't work, try manual installation. I don't know why, but this is a bit fiddly at this point :/