Holy Warlock Archer-question about radiant soul

[ImproperJustice]

I am working on a concept of a Celestial Archer, using Warlock and greater pact weapon.

Going for flavor over optimization, but I was curious about Radiant Soul and it’s interaction with some higher level spells.

It says:
Startingat6thlevel,yourlinktotheCelestialallowsyou toserveasaconduitforradiantenergy.Youhaveresistanc etoradiantdamage,andwhenyoucastaspellthatdealsradi antorfiredamage,youcanaddyourCha-rismamodifiertooneradiantorfiredamagerollofthatspe llagainstoneofitstargets.

So if I cast say: Crown of Stars or Investiture of Flame, will this boost the damage of their effects?
Crown of stars lets you shoot Motes of light for 4d12 radiant, and Investiture shoots flame or burns targets close to you.

But does that fit the definition of “when you cast the spell”. Or like most things in 5e will it just be a GM judgement call?

[Degwerks]

I believe you can only do it one time per cast of the spell. So in your instance of Crown of stars, only 1 shot from that hour long spell will get it. Fireball would give it to everyone, wall of fire would be everyone, 1 time. Same with Flaming Sphere. Just only once.

[JackPhoenix]

I believe you can only do it one time per cast of the spell. So in your instance of Crown of stars, only 1 shot from that hour long spell will get it. Fireball would give it to everyone, wall of fire would be everyone, 1 time. Same with Flaming Sphere. Just only once.

It's once per spell, to one target. Fireball and Wall of Fire would do the extra damage to one creature only.