What is a 'LUT'?
Answer: Well, 'LUT' stands for 'LookUp Table', though in the context of this mod it refers to a 'Color LookUp Table' (sometimes called a 'cLUT'). These were added to version 0.18 for handling how colors change at night, when wearing night vision goggles, and so on in a more moddable way.

So, does this mod basically make night time more 'realistic'?
Answer: Essentially, yes.

Does that mean it'll be even more difficult to see at night?
Answer: Nope! The default LUTs don't account for how human eyes perceive and balance colors under different light sources. The result is that everything is tinted blue at night, and by an amount that makes it harder to tell the difference between things that are meant to be. For example, orange and red: the orange is now dark purplish pink, and the red is just a sliiiiightly deeper purplish pink.

With these LUTs, the perceived difference between hues should more or less match up to how our eyes would perceive those same differences, when objects of those colors are placed under a light source that's more blue. Because of this, the contrast between colors is easier to see, improving visibility. Additionally, the exact hue of blue at night is less extreme than the default LUTs (though I did go with the most extreme form of blue that was still a proper daylight color).

Edit: Maybe, depending on your monitor. I've proposed a possible change in the LUTs provided in the mod in the discussion section, and would like some opinions on the proposed new LUTs!

What do the screenshots show?

1. The first screenshot in the gallery on here shows how night looks with the original, vanilla LUT.
2. The second one shows how night looks with my LUT.
3. And the third shows how it looks sometime around sunset. There's no specific length of time that's guaranteed to have the sunset LUT applied by itself, but it's hopefully close enough to see the effect.