First, I'd recommend experimenting with the terrain fog in Scenario > Map Options, and seeing if you can get the effect you want:
All about fog You are having troubles getting that fog to blend in with your terrain? No matter what you do, the colors just don't fit in? Your fog looks unnatural? This brief tutorial may help. 1. Fog options In order to use the fog, you need to enable it first. Fog options are accesed...
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It won't actually affect the
lighting, but a lot of maps will use fog in combination with the default lighting models to affect the "look" at night. I recommend also going to File > Preferences > Visual and changing the time of day in the editor to midnight to see what things look like at night.
I'd recommend finding one set of values that looks good during the morning, one set of values that look good during the day (i.e. usually a lot clearer), and one set of values that look good at night. Then you can use triggers to set the terrain fog periodically and go between those values. If you'd like, I can share an example of what those triggers would look like.
If you do want it to actually get
physically darker, then you will want to look into using a custom animated DNC light model:
Animated DNC Light Models DNC (DayNightCycle) is a model made to simulate day/night cycle behavior. It occured to me, one day, that I could make one with much more contrast than the original, Blizzard ones, have. I started editing values in Magos' model editor, just to realize that the editor...
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These models contain some lighting information and you can customize it to get the look you want.
EDIT: Here is a sample map that combines the two things above (fog and a custom DNC model) to sorta demonstrate some of the possibilities.
If you want to play around with it, try editing the "FogConfiguration" trigger. If you want to edit the DNC model, you can take a look at the tutorial linked above and try tweaking the model to the values you want. It'll look like this in-game:
