I get what you're saying, but I assumed (possibly incorrectly) that the DC value accounted all those points? After all, the trap is meant to be hidden so lighting, etc shouldn't make a difference (it's captured in the players passive perception).
And if they're looking for it, they're no longer using passive perception anyway....
Here's the problem with this entire thing. Bounded numbers mean that a 1st level party generally has PP somewhere between 9 and 16. This is only a 7 point difference. Also, the spread is normally less than that. So far, it's been my experience that the "practical" spread is between 10 and 14.
Which means, that when you are making up a trap and setting a DC, you are purposefully choosing how many of the party members can spot the trap passively. This is especially bad when you are writing an adventure specifically for one group of players you already know their PP. Let's assume you are writing a generic adventure that you plan to run multiple times or publish.
If you set the DC at 17 or higher you are saying that the trap can never be spotted.
If you set the DC at 15 or 16, you are essentially saying that most groups will not be able to detect it at all. Only those with a super specialist will detect these traps.
If you set the DC at 13 or 14, you are essentially saying that the trap will be immediately spotted by all groups except the ones lacking all Wisdom based classes.
If you set the DC at 12 or lower you are saying that all groups everywhere will spot it immediately. It essentially isn't hidden.
It takes all the randomness out of finding it. I'd like a system that says "Your character has keen eyes and is on the lookout for trouble, therefore you have a better chance of finding this trap than a different group that doesn't have someone as keen eyed in it." But the key words in there are "better chance". There should be a chance but we need a die roll in order to model all the things we're uncertain about. How distracted is your character? Did your character happen to look in the exact right place to notice the details he needed to? That kind of thing. That's why we normally use die rolls for skills, to prevent the binary nature of "Sure, you're good enough, you succeed all the time."
Unfortunately, in this situation, you don't want to tip off the players when you are rolling to see if they spot traps. So the die roll needs to be made by the DM. When Mike Mearls posted that traps would all be rolling their stealth checks against the PP of the party, I jumped for joy because this seemed like the simplest and easiest solution to this problem. I'm very disappointed that it got lost somewhere along the line.
I think if I use this system there's only 2 ways this goes:
1) The PCs spot the traps 100% of the time. Most adventures will read like this: "You walk down the hallway, you spot the trip wire and step over it. You spot a trapped stone slightly past that and be sure not to step on it either."
2) I will set the DCs too high for PP to work and then the PCs will be forced to roll continuously. That'll end up like this: "A hallway? I assume its trapped. I search. I roll 15." "You don't find anything." "Yeah, 15 is too low to spot traps, I obviously failed. Everyone else in the party searches the hallway as well. The highest is 22." "*sigh* Yes, you find all the traps. You continue on to the next room." "A room? I assume that's trapped too. Everyone make checks!"