We've generally run it as
Moonlight = concealment (20% miss chance)
Starlight = improved concealment (40% miss chance)
and under the trees the light level goes down one step - if it's full moonlight out in the clearing, it's starlight under the trees.
As to "how far" - outdoors, basically as far as is lit and not blocked. On a moonlit plain you can see quite far. In a forest your sight line is blocked by the surrounding trees pretty quickly.
OT, I've always wondered why Monstrous Humanoids ("humanoids with animal-like features") all get darkvision. Flavor-wise, I'd expect them to have low-light vision, like creatures of the Animal type. And for that matter, why is a grimlock, derro or hag a monstrous humanoid while merfolk, gnolls, kobolds, troglodytes and lizardfolk are not? Why is a ranger who takes Favored Enemy: Monstrous Humanoid equally effective against creatures as diverse in their anatomy and habits as harpies, centaurs, and sahuagin, while one who takes Favored Enemy:Halflings gets no bonus against gnomes or humans?
