Both Illumination Within and Animated Window Lighting System (which you can use simultaneously if you want IW's light sources on vanilla buildings and AWLS's versatility) show up just fine with All Natural and Immersive Interiors installed, when you're outside. But if you're inside a building, looking out through a window at the city Immersive Interiors has added, you have to use AWLS if you want to see other windows lit up at night. So either, or both, are fine when you're outside, but only AWLS works when you're inside. It's pretty damn impressive looking out at the city and being able to see a bunch of windows on other buildings lit up, considering how far beyond the vanilla game it is.