[jp10]

As I look at it...

If one wishes to set a consistent system for night visibility I believe this topic is lacking a baseline assertion to frame the issue. While the numbers can vary by argument they should follow a logical pattern. There are many assumptions which are not spoken because the type of weather and moon condition in a battle is only interpreted by visibility range and not an editor setting.
Base calculation night full moon.
1. The base number of visible hexes should be night with full moon on flat featureless terrain like a sports field.
2. The worst weather types possible would be a number value that would reduce the base number to 0-1 hexes.
3. The 'normal' or average weather types possible would be a number value that would reduce the base number to half value.
4. No weather would be the same as the base number.
5. The weather types between worst and normal would be 1/4 the base number.
6. The weather types between normal and no weather would be 3/4 the base number.

Calculations for night/no moon would be done in the same manner. Night/half moon should roughly be at 50% values to night/full moon and night/no moon. 1/4 and 3/4 values would be properly proportional.

Some terrain would need special weather types, i.e. desert terrain might have mirage effects and tropical jungles might have a 'high humidity haze' that reduces the max range.

No adjustment should be made for terrain since that would be a function of the map terrain. A night that you should be able to see 100 yards is not 'darker' because there is vegetation blocking your line of sight at 50 yards. There is just a bloody big bush in your line of sight.
Unit/vehicle size changes to detection in the dark is a function of the game's 'unit size' values.
The night visibility ranges do not need to be changed if your scenario involves 'sneaky recon units' or 'creeping snipers'. That is a game calculation by unit type.
The game would account for night vision technology (but not trip flares or illumination rounds) by applying the values of a unit's rangefinder/vision ratings.
Unit movement or a unit firing weapons giving a greater detection chance would also be applied by the game. No adjustment to the night/weather values need be considered.

The only changes to these night values would be a scenario specific circumstance but it would be a factor that worked for both sides.