Attacking a target in dim light, from darkness, at great distance

Question

Character A is in Darkness with no Darkvision

Character B is in Dim Light a hundred feet away from A

For further context, an ascii board (dashes indicate dimly lit area):

                    -B-----
                  -----------
 A               ------L------
                  -----------
                    -------

|        100 ft        |

Are any penalties imposed on A's Ranged Attacks?

I've been looking around, and the closest thing I can find is this: How far away can you see light? which tells me that Character A can definitely clearly see the light source.

Does this mean that they can also see the dimly lit character just fine, and make attacks as normal (provided their weapon is in range)?

In that case, does this mean that (not only can they attack without penalty) but they get advantage on their attacks due to being hidden by darkness?

Answer 1

[Note that the interaction darkness-->obscured-->blinded was subject to an erratum; if your PHB is an early printing this answer may look contrary to your rules.]

When you are in darkness someone trying to see you is "effectively blinded" but you are not (PHB p.183, "Vision and Light," errata'ed). Since you are unseen your attack roll has advantage (PHB p.195, "Unseen Attackers and Targets"). But your attack roll against your target--who is lightly obscured--is not affected (PHB p.183, "Vision and Light").

Therefore you attack with advantage. Yay!

(You ask if "they can also see the dimly lit character just fine, and make attacks as normal? " Attacks are normal, but they don't actually see the dimly-lit character "just fine": their perception checks into the dimly-lit area would be disadvantaged, per "Vision and Light.")

Answer 2

If B cannot see A, A can attack B at advantage

A can see B

A is in darkness which means that they suffer the blinded condition only when trying to see anything only in the darkness around them per the definition of darkness which creates a heavily obscured area.

Darkness creates a heavily obscured area. (PHB 183)

A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature effectively suffers from the blinded condition when trying to see something in that area. (PHB 183)

Since B is not in darkness but is in dim light, A can see B. Here is what the DMG has to say about the limits of vision:

When traveling outdoors, characters can see about 2 miles in any direction on a clear day, or until the point where trees, hills, or other obstructions block their view. Rain normally cuts maximum visibility down to 1 mile, and fog can cut it down to between 100 and 300 feet.

So as long as there is a light source and sight has not been blocked by anything, A should have no issue seeing B even at great distances.

If B cannot see A

If B does not have darkvision beyond 60 feet or does not have it at all, then B cannot see A standing in darkness.

A is standing in darkness, thus B (who has no darkvision) cannot see them.

Since A can see B but B cannot see A, when A attacks their attack will follow the rule for "Unseen Attackers and Targets":

When a creature can't see you, you have advantage on attack rolls against it. (PHB 195)

Thus A's attacks against B will be made at advantage.

If B can see A

If B has darkvision out to 120 feet or some other means of seeing in darkness at A's position 100 feet away, then A is visible. If A is visible, then they do not get any advantage on attacks against B.

The dim lighting does not affect attacks at all

Because the area around B is in dim light the area counts as a lightly obscured area. However, a lightly obscured area has no effect on attacks, only perception checks.

Dim light, also called shadows, creates a lightly obscured area. (PHB 183)

In a lightly obscured area, such as dim light, patchy fog, or moderate foliage, creatures have disadvantage on Wisdom (Perception) checks that rely on sight. (PHB 183)