This isn't a question about the vampire class - it's about vampire monsters, e.g. Master Vampire or Elder Vampire Spawn. In both of those monsters, it says they are damaged by direct sunlight:
Whenever the vampire starts its turn in direct sunlight, it takes 10 radiant damage.
I assume that since it did not say radiant, nor is the monster vulnerable to radiant, any generic radiant damage that my players deal to it does not trigger this trait.
However, one of my party members possesses a Sunblade Fullblade. The flavor text on that weapon reads:
This heavy golden sword attacks with the power and intensity of the sun, burning nearby enemies.
Its powers specifically say it deals radiant damage. So the question is, does an attack using this weapon count as "direct sunlight"?
Furthermore, there are two other powers to this weapon:
This weapon can shed bright or dim light up to 20 squares. You control the brightness and range of the light.
You cause motes of light to burst out and attach to your enemies. Make an attack: Close burst 1; targets enemies; Strength vs. Reflex (apply a bonus to the attack roll equal to the weapon's enhancement bonus); on a hit, the target takes 1d8 radiant damage.
Would either of those also count as direct sunlight with respect to vampire damage?