Upvoted.
I foresee a problem with this, and it's perhaps why they did it this way in the first place. When in a normal vehicle there is a fair amount of outside light let in. A tank, on the other, lives up to its name thus seals off all outer light. unfortunately, the engine doesn't create this very well. A totally sealed off internal volume still has day lighting in this game, such as tanks and buildings. Go into a closed room in one of the buildings and notice you can see without lights on.
So the work-around might be something like this: make the default lighting set as utter darkness, and let lights do the lighting (eg flashlights, headlights, etc). Make the SUN a very big, distant, bright light, and add a parameter within a volume (simulating the air) to brighten up the shadow areas. Then perhaps add extra volumes within a space, like a building, that supersede the parameters of the main air volume. As you open a door or hatch to the outside, the strength of the internal volume darkness becomes weaker.
For tanks, this is a simple solution to a problem, but for buildings with multiple rooms, this can get very complex. Let's say you had an unlit building with two big rooms. Room1 is accessed from a door that leads outside, and room2 is accessed from a door to room1, which is open. Main door is closed, and all is dark. Standing in room2 the main door is opened, and room1 becomes much brighter. Cool, but how do we keep room2 from getting flooded with all that light?
Figuring this all out sounds very taxing on processors. You might be able to make tank interiors which use much darker textures, but how would that look when the hatch is opened? To see the lighting problem, try downloading the Burnes Armory mod, which has tank interiors.