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How should you handle rolling for perception in areas with different levels of obscurement? E.g in darkness illuminated only by a torch (20ft bright light and 20ft dim light beyond that) or on a field with "moderate foliage" or "patchy fog" only in certain areas?

Consider the following common cases:

  • A character standing guard in torchlight while the others are sleeping: Should they roll their perception check with disadvantage because an enemy will be approaching through the dim light, even though other things might happen in the bright light which should be caught by the same check, for example a rat stealing some rations from their backpack?
  • A character wanting to look out for traps as they move through a dungeon, where a hidden wire or pressure plate would first come into view in the dim portion of torchlight before entering the bright area. Do they roll normally and simply not notice anything in the dim light? Should the DM subtract 5 from their roll for the dim area?
  • A character wanting to examine a wide field with moderate foliage in a few patches for any sign of enemy activity, where a goblin is hiding in one of the bushes and faint tracks of goblins in the grass? Should the singular action of examining the field be divided up into multiple rolls for each part?

The question is only about active Perception checks as called for by the players (for passive checks, the rules are clear, as per Dale M's answer).
I am especially looking for official rulings or suggestions on how to handle cases such as this or examples from someone who has come up with a working system (or a way to avoid such checks in the first place).

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  • \$\begingroup\$ When in the bright light, or not covered by the fog or foliage how are your hidden things remaining hidden? \$\endgroup\$
    – SeriousBri
    Nov 6 '21 at 15:15
  • \$\begingroup\$ @SeriousBri so many ways: rpg.stackexchange.com/q/63441/6203 \$\endgroup\$
    – Dale M
    Nov 6 '21 at 20:37
  • \$\begingroup\$ @DaleM none of that shows me how to be hidden with nothing to hide behind, unless counting invisibility, which I would assume the question would mention as it makes light and obscurement irrelevant. \$\endgroup\$
    – SeriousBri
    Nov 6 '21 at 20:40
  • \$\begingroup\$ @SeriousBri The sniper in the photo is not hiding behind anything. They are using camouflage. \$\endgroup\$
    – Dale M
    Nov 6 '21 at 21:15
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    \$\begingroup\$ I will try to clarify the question in the morning. But for the moment, consider a goblin hiding in the bushes and a player wants to look over the entire area for enemies. Do they roll with disadvantage because the enemy is obscured or roll normally because they are also looking at an area not obscured? \$\endgroup\$
    – Jave
    Nov 6 '21 at 23:11
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There are no rules for resolving multiple DCs some with and some without disadvantage - use multiple checks or passive checks

Example 3 is the tricky one here, but I will cover the first two anyway. You said not to use passive perception, however both of those two examples should be resolved using passive checks as per the rules.

Refresher on passive checks:

A passive check is a special kind of ability check that doesn't involve any die rolls. Such a check can represent the average result for a task done repeatedly, such as searching for secret doors over and over again, or can be used when the DM wants to secretly determine whether the characters succeed at something without rolling dice, such as noticing a hidden monster.

Example 1

A character standing guard in torchlight while the others are sleeping: Should they roll their perception check with disadvantage because an enemy will be approaching through the dim light, even though other things might happen in the bright light which should be caught by the same check, for example a rat stealing some rations from their backpack?

When standing guard you are doing something continuously, and should use a passive check. So in this case you don't have to make two rolls, instead you use passive perception and compare that to the stealth check (or DC if the enemy is not stealthy) of the enemy they may notice. When the enemy moves into the light the passive perception increases as the penalty is removed.

Example 2

A character wanting to look out for traps as they move through a dungeon, where a hidden wire or pressure plate would first come into view in the dim portion of torchlight before entering the bright area. Do they roll normally and simply not notice anything in the dim light? Should the DM subtract 5 from their roll for the dim area?

Normally you would use a passive check for this rather than using an active check. As the trap becomes more well lit the passive check is adjusted and the trap may be revealed.

Example 3

A character wanting to examine a wide field with moderate foliage in a few patches for any sign of enemy activity, where a goblin is hiding in one of the bushes and faint tracks of goblins in the grass? Should the singular action of examining the field be divided up into multiple rolls for each part?

This is the real problematic situation. The goblin is lightly obscured, while the goblin tracks are not. As such, you want to make a roll which covers both searching for the tracks with a normal roll and searching for the goblin with a roll at disadvantage. Unfortunately there are no rules which allow that kind of check to be made.

The problem here is the granularity of the rolls. The player is asking to do two things with one roll: search the grass, and search the bushes. By RAW you make one roll for one thing. So, break it down to two rolls; you can search the grass, then search the bushes at disadvantage.

While making multiple checks works ok for this example, it can be awkward as the scale increases. For example:

Two items are lightly obscured, one in a tree far away, one in a barrel close by, while a third is not obscured lying in the grass.

It feels strange to ask the player to roll once to search the grass, then a second time to search the barrel and the tree since those are unrelated objects far apart. It also feels a bit excessive to ask them to make 3 rolls - or more if there are more barrels/trees in the area and you don't want to tip them off as to where the items are.

However, 5e has mechanics for resolving "a lot of rolls"; passive checks. If the character needs to search a whole bunch of places, then just use a passive check. There are no guidelines as to when you should switch from active checks to passive checks other than that they are "average result for a task done repeatedly". I would suggest that if your resolution feels unwieldly then you have passed that threshold.

Remember Stealth provides equivalent bonuses

Keep in mind the rules for advantage:

The DM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result.

Generally speaking being in darkness or in dense foliage is a circumstance which is advantageous to being stealthy. In example 3 above, the goblin is hiding in bushes and thus is at least lightly obscured. As such, they will be making their stealth check with advantage.

While it is true that the goblin will also be harder to perceive than the tracks due to the bushes, you should keep in mind that the goblin has already gotten half its bonus. A DM who is playing fast and loose with the rules could simply ignore the problem in Example 3 and ask the player to make a normal roll. Since the goblin hid with advantage they will already be somewhat more difficult to find than the tracks.

Personally I do not do this, as I want the goblin to be just as hard to find whether or not there are tracks. But if this situation comes up once in your entire campaign, it may be beneficial simply to make a quick and decisive ruling rather than digging deep.

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  • \$\begingroup\$ At our table we have always used the guide that when a player calls the action they want to take, any check is treated as active and when a roll is needed but no action (or a different action) has been called for it is treated as passive. But it seems that we may have to revise this "rule". \$\endgroup\$
    – Jave
    Nov 12 '21 at 11:46
  • \$\begingroup\$ @Jave If it's working for you except for in this case, you may be better of just asking for two checks: "make a check to search the grass, and one at disadvantage to check the bushes" Follow your heart mate, there's now wrong answer. \$\endgroup\$ Nov 15 '21 at 2:09
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Is it an active or passive check?

In both cases they have disadvantage in the lightly obscured area and not in the brightly lit area if they are relying primarily on sight. If it’s heavily obscured they also have disadvantage if they can perceive it at all (e.g. it makes a noise, or smells, or the PC is groping for it).

For an active check use 2 distinguishable d20s which, for want of better terms we’ll call the first dice and the second dice. For the brightly lit area the PC’s roll is what the first dice shows and where they have disadvantage it’s the lower of the two dice.

For a passive check, disadvantage reduces their passive perception by 5.

This is just the most straightforward application of the (dis)advantage and passive check rules.

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  • \$\begingroup\$ Is that 2d20 advice official, or just how you do it? \$\endgroup\$
    – SeriousBri
    Nov 6 '21 at 20:41
  • \$\begingroup\$ @SeriousBri I linked to the applicable rules \$\endgroup\$
    – Dale M
    Nov 6 '21 at 21:16
  • \$\begingroup\$ The question is about active checks since the passive case is trivial as stated. I do like this answer though for its simplicity! \$\endgroup\$
    – Jave
    Nov 6 '21 at 22:03
  • \$\begingroup\$ Dale M, I'm not quite following, are you saying that this method of rolling two d20s and using them to make a normal check and a check at disadvantage at the same time is RAW? It's definitely an interesting ruling, but I have never heard of or seen anyone do this, and I can't see where it is suggested in your link. \$\endgroup\$ Nov 9 '21 at 2:59
  • \$\begingroup\$ @MagicalItemSmith the RAW say “roll a second die” which is what the answer says. \$\endgroup\$
    – Dale M
    Nov 9 '21 at 3:43
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Passive checks exist for situations like this.

It might feel weird to not ask each player in turn to roll Perception, but this is the sort of situation that passive checks were designed for - in your first example, the PC stands guard for an extended amount of time, while the creatures sneaking up roll Stealth against their passive score - normal passive score for the rat in torchlight, and passive score minus five (because of how disadvantage and passive checks interact) for the enemies.

The players cannot call for a check.

Slightly tangential, but also important - the players describe what they want to do, the DM asks for any checks that might involve. The oft heard "can I roll [skill] to [action]" is not RAW.

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  • \$\begingroup\$ Re: your last paragraph: At our table we have always been playing that when a player describes the action they want to take, any check that might be involved is rolled as active, and when a roll is needed but no action has been called for, passive is used. But I see now that we might have to revise this. \$\endgroup\$
    – Jave
    Nov 12 '21 at 11:43
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You can't hide in the open

What you are describing seems to me like you have areas where someone (something?) can hide, and some areas where they can't.

The source of being able to hide is either darkness, or light obscurement, and when they leave these areas - entering the light or the open - they no longer have a way to hide.

As soon as they move into the open or lit areas they will be automatically spotted by anyone looking.

What changes here is the ability to hide, not the ability to perceive.

So how do I handle this?

Make a check with disadvantage to try and spot the target in the obscured section, but no check at all if that target happens to wander out in to the open. It just happens.

Related rules: Hiding (PHB p.177)

When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding, that check’s total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence.

You can’t hide from a creature that can see you ...

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  • \$\begingroup\$ A great addition, and a guard with their back turned for example would be a case of perception through hearing and thus not subject to disadvantage. However other things than enemies might be hidden such as a secret door or a pressure plate. \$\endgroup\$
    – Jave
    Nov 6 '21 at 22:05
  • \$\begingroup\$ A guard with the back turned isn't actually guarding very well and they wouldn't be making active perception checks, most likely making passive checks with a situational disadvantage imposed for not paying attention. There is a similar situation in LMoP where the goblin guards get disadvantage because they aren't guarding very well. \$\endgroup\$
    – SeriousBri
    Nov 6 '21 at 22:49
  • \$\begingroup\$ I meant actively turning around to make it harder to sneak up behind him, but the method of guarding is unrelated to the question. The question is about how to handle when what should probably(?) be a single check has both disadvantage and not. \$\endgroup\$
    – Jave
    Nov 6 '21 at 23:18
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    \$\begingroup\$ The first part of this answer is wrong. The PHB errata states “The DM decides when circumstances are appropriate for hiding.” and “You can’t hide from a creature that can see you clearly …” Bright light and no cover may be a necessary conditions but they are not sufficient. Torchlight is not daylight and while they both create bright light a reasonable DM could easily rule that you can hide (or remain hidden) in the former and not the latter because you cannot be seen “clearly”. \$\endgroup\$
    – Dale M
    Nov 7 '21 at 0:18
  • \$\begingroup\$ The DM decides everything, are you suggesting that it is reasonable to walk through torchlight and not get seen if someone is looking? \$\endgroup\$
    – SeriousBri
    Nov 7 '21 at 10:28

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