I have a question about the magic effects inherent in light and darkness in d&d 5.
Within an area subject to Darkness (spell level 2) if I wield a sword that magically emits light, the light is not affected by the spell. My question is what happens if have a magical effect of Darkness versus a magical effect of light or dim light?
Darkness says:
nonmagical light can't illuminate it.
[...]
If any of this spell's area overlaps with an area of light created by a spell of 2nd level or lower, the spell that created the light is dispelled.
...so as you indicate, non-spell magical light is unaffected.
That said, darkness is not dispelled unless a specific effect says it would be. For example, the daylight spell sas:
If any of this spell's area overlaps with an area of darkness created by a spell of 3rd level or lower, the spell that created the darkness is dispelled.
If this type of text is not present, the magical darkness is illuminated just like regular darkness by the magical light, but the darkness is still present, meaning that snuffing the magical light returns the magical darkness in spite of nonmagical lights.
There are a couple of lines that clarify how magical light and magical darkness from the spell interact.
The first one is (emphasis mine):
A creature with darkvision can't see through this darkness, and nonmagical light can't illuminate it.
So, actually, the sword (being magical) can break the darkness spell.
The second bit is the following:
If any of this spell's area overlaps with an area of light created by a spell of 2nd level or lower, the spell that created the light is dispelled.
Hence, a Cleric who casts the Light cantrip while inside the Darkness' AoE cannot illuminate the area.
On the other hand, other spells can successfully counteract the Darkness spell: for example, Daylight:
If any of this spell's area overlaps with an area of darkness created by a spell of 3rd level or lower, the spell that created the darkness is dispelled.
