What do people mean when they say the lighting is "realistic" taking consideration the distance to the sun and etc.?
I ask this very seriously (and curiously). Do you mean to say that ambience is zero when there is no planet nearby, and non-zero when there is one? I am pretty satisfied with that decision.
Do you mean to say that in missions where the sun is distant, then the lighting should be very very small? That's pretty unjustified to me. The reason being because our eyes are so adaptive you cannot really compare a situation near Earth to a situation far away directly. Because the screen is limited to 24 bits (and I'm sure the calculations of lighting are also constrained to 24 bits, correct me if I am wrong), the adaptiveness of our eyes is lost on both the lack of contrast and the amount of calculations per pixel (which degrade the image to a very far below 24 bits "quality" in the end).
A much more compelling differentiator would be a very wide range of contrasting colors near Earth (or the Sun for that matter) and when you want to convey darkness, instead of going "full dark" which is somewhat annoying, you can go "near-full black and white" with post-processing or something of the sort. The idea here is to convey that the eyes have indeed adapted to the darkness of the sky (with the sun far away), but at the cost of color perception (which is what realistically happens to our sight when the ambient is very dark).
Or perhaps BP already does some of this, and I'm going overboard here. But I agree that the darkness of BP is sometimes off-putting.