In Volo's Guide to Monsters, the Aasimar playable race has the following trait (pg. 105):
Celestial Resistance. You have resistance to necrotic damage and radiant damage.
So they take only half damage from radiant damage.
The Scourge Aasimar sub-race also have this ability (pg. 105):
Radiant Consumption. Starting at 3rd level, you can use your action to unleash the divine energy within yourself, causing a searing light to radiate from you, pour out of your eyes and mouth, and threaten to char you.
... at the end of each of your turns, you ... take radiant damage equal to half your level (rounded up). In addition, once on each of your turns, you can deal extra radiant damage to one target when you deal damage to it with an attack or a spell. The extra radiant damage equals your level.
So let's say a level 10 Scourge Aasimar activates this ability. During their turn, they make a nearby creature take 10 radiant damage. Does the Aasimar themselves take 5 also, or do they only take half of that because of their Celestial Resistance?
In other words, does their Celestial Resistance negate (some of) their own self-dealing damage from Radiant Consumption?