That's the realism of Arma 2. If you go out on a field (IRL) where you only see some lights far away, the ground and your surrounding is pitch black. It's all realism. If it's a clear sky with a moon that's shining over you, the moon will reflect the sun and voila! the night will be brighter. But as this is a "Scary" mod, the weather will be bad most of the time. Hence the black night