Hiya!
Is the same true for rogues being within the range of non-darkvision monsters in dim light? I.e., is it possible for a rogue in your game to sneak up close to a castle guard and then sneak away again?
Seems to me that ruling that out suggests that the monster/guard does nothing but stare in the direction that the rogue will be coming from.
I guess I didn't write that very clearly in my post...sorry!
What it boils down to for me is this: no light = no 'place to hide' (e.g., shadows).
Maybe don't think of it as "dim light", think of it as "brightly lit with no shadows". Can someone sneak up on someone in the middle of a field with a noon-day sun in the sky and no clouds in the sky? Yes...as long as the person doesn't look in the direction of the sneaking thief. Same with Darkvision. If it was totally dark ("totally light"), the only thing keeping the thief from not being seen is if the guard doesn't look in his direction. If he does...the jig is up.
Now, if there are places to hide
behind, like a big crate, lets say. Then yeah...but at that point the thief isn't making any Stealth check...he's just hiding behind a big crate. The lumbering barbarian with a 5 dex would be 'hiding' just as well as the thief...because, well, they are 100% CONCEALED (so don't need to make a 'hide' check).
So, in essence, a darkvisioned thief trying to "scout" ahead with no light sources around is gambling. He's hoping that if he rounds a corner, that there isn't anything there...or looking to where he is. If they are...he's spotted. Period. It might have well have been a brightly lit corridor with a non-darkvisioned thief walking around the corner. However...put a party of adventurers with a torch behind that thief...aaaahhhh.... Now the monsters see a torchlight coming from up around the bend, so they get ready to shoot their bows at the carriers! However, the thief is 'scouting' ahead of the party...he peaks around the corner and...can make a Stealth check to quickly pop his head back before being seen by the baddies with bows. He can then go tell his party that two hobgoblins with bows are around the corner. Why? Light.
At least, in my campaign. IMC, "light" trumps "darkvision". If something has darkvision, but there is light, that creatures 'normal vision' kicks in...meaning it effectively has no 'darkvision' (it's switched off, so to speak). Get rid of that light source and *click*...darkvision kicks in.
Make sense?
^_^
Paul L. Ming