There are instances in which the use of perception can be confusing. When a rogue is sneaking up on a fighter and rolls his stealth check, but the acoustic modifiers are different from lighting modifiers, which should be used? What if the fighter is an elf with a +2 to Sight - can it be used in the perception roll to detect the rogue?
I think it would be best to separate Perception into Sight and Hearing as two separate skills, but I doubt that's going to happen, even though that would also solve the issue of the skill being too powerful now, so I will try to make a suggestion working within the current system.
Method 1:
Perception is rolled using a sense that has the lowest DC to detect the creature or object in question.
Method 2:
Same as method 1, but other senses can decrease the DC by 1 point each, if they could also be reasonably used to detect the creature/object and if they are within 5 points of the original DC as used in method 1.
I deliberately made the roll dependent on the lowest DC and avoided the more accurate solution of making the roll the one that is the most likely to detect the sneaking creature, because this would also depend on the bonuses the detecting character has to his senses and this would not only make things more complex, but might call for a different sense being used by different party members.
Example of Method 1: The DC to visually detect the Rogue approaching our above-mentioned Fighter is 15. The DC to detect him acoustically is 18.
The Fighter will therefore roll Perception against DC 15 to visually detect the Rogue and ignore acoustics altogether.
Example of Method 2:
The situation is the same as in Example 1, but we modify the Detectability DC by 1 from 15 to 14, because the Rogue can also be heard (at DC 18, which is not 5 pointshigher than the sight DC of 15) with not much greater difficulty than he can be seen. If he also reeks of sweat and blood after having fought a battle against the guards before his sneaking attempt and we decide that his DC to be detected by smell would be 19, the Detectability DC decreases by a further point to 13. Senses like taste are simply not applicable here, because the Rogue cannot reasonably be detected by being tasted, so they cannot modify the DC.
Of course, when the DM decides that only one sense can reasonably detect the sneaking Rogue, the Detectability DC is based on that sense alone and not modified by others.