How do vampire (monsters) take sunlight damage?

Question

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.

and

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?

Answer 1

When a vampire starts its turn in direct sunlight (literally sunlight, nothing else), then that monster feature is triggered. Nothing else triggers it, because 4e rules do only and exactly what they say they do.

When it triggers, the vampire takes 10 damage. It so happens that this damage has the radiant type, but that doesn't do anything special by itself and doesn't have any effect on when the feature triggers. Because it has a type someone can take advantage of it (say, if an PC's attack adds a vulnerability to radiant damage to the target), but it does nothing by itself.

All the other things in your question have no connection to the sunlight-triggered damage effect, because they don't satisfy the literal meaning of the trigger. Only an ability that conjured literal sunlight and made it fall directly on the vampire's square would trigger the damage. A very bright light doesn't cut it, even if the power's descriptive fluff says it's as bright as the sun – it has to be actual sunlight, not just "the power and intensity" of the sun.

Lastly, radiant damage from other sources doesn't interact with the vampire's sunlight feature because radiant damage is not part of its trigger, only its effect.

Answer 2

First off, you are correct that radiant damage does not trigger the vampire's "direct sunlight" drawback feature. The reason for this is that "sunlight" is not a keyword, while "radiant" is. Radiant damage has nothing to do with the sun, as can be seen by its use in powers flavored as moonlight, starlight, holy energy, and other non-solar effects.

Now, to the meat of your question, which is related to the above idea. The main rule here is that:

Flavor text has no mechanical value.

A power’s flavor text helps you understand what happens when you use a power and how you might describe it when you use it. You can alter this description as you like, to fit your own idea of what your power looks like. Your wizard’s magic missile spell, for example, might create phantasmal skulls that howl through the air to strike your opponent, rather than simple bolts of magical energy.

When you need to know the exact effect, look at the rules text that follows. (PHB1 p55)

Since the only mention of sunlight in the Sunblade's text is in its flavor, and not in the rules text, then the Sunblade is not considered sunlight under any condition.