Light, Darkness and Vision

[Wids]

  

One thing which was never made perfectly clear for me was how light and darkness affect adventurers, creatures and adventuring in Neverwinter Nights.  I can't find anything on the Wikia to answer my questions, and while this server (and others like it) impose certain penalties on items with Light properties (ie. the common -10 penalty to Hide here), just the fact that some items on this server don't include that penalty to Hide indicates that such penalties aren't in themselves inherent to carrying a light source around.

So, questions:

1)  Are there any hidden bonuses or penalties to being in lit areas and/or carrying a light source (not counting the artificially imposed Hide -10 penalty on some items)?
1a)  If any such adjustments exist, are they affected in any way by the brightness of the light source (ie. Dim, Low, Normal or Bright)?
2)  Are there any hidden bonuses or penalties to being in dark or unlit areas without a light source?
2a)  If any such adjustments exist, do they change depending on whether or not the creature has some superhuman kind of vision that penetrates darkness (ie. Lowlight Vision, Darkvision, Ultravision, True Seeing)?  If so, how?
3)  Otherwise, is a character in perfect darkness without any kind of superhuman vision just as capable of attacking and striking an enemy as they would be in a brightly lit room?  Is a light source purely a cosmetic benefit, or does it actually help in some way (and thus justify the common Hide -10 penalty here)?
4)  Functionally speaking, what are the mechanical differences between Darkvision and Lowlight Vision?
5)  Is Ultravision nothing more than Darkvision which ignores Darkness spells (at least in theory)?


Thank you. 

[Wids]

I'm bumping this because I just took Viora out hunting again. Viora has a Ring of Crimson (the Bioware kind which gives you 15 meters of red light without any -10 to Hide in its properties), and I noticed that the baddies almost always saw through her stealth-walking and came running to attack, even when they were outdoors (Trackless Step be damned). But as soon as I unequipped her Ring of Crimson, she started getting the drop on goblins, kobolds, bandits and whatever else from time to time.

Is this cause-and-effect (to wit, all light sources come with a hidden penalty to those hidden Hide checks), or is it mere coincidence (to wit, Viora just so happened to start acing her Hide and Move Silently checks as soon as I removed her ring, with no actual correlation between the two events)?