I'd say no.
The extra radiant damage is from the zone created by ToL.
OS does not gain the Radiant keyword.
Its an open and shut case.
Keep in mind that was a quote from the PHB1, back before they added in all sorts of trickiness... back then a power that did acid damage DID have the acid keyword. I view that more as a descriptive sentence than a mechanical rule. I'm of the view that unless you obtain the radiant keyword explicitly from somewhere (eg radiant weapon), its not a radiant attack, even if you do a little radiant damage.Is PHB p55 considered declarative:
For instance, a power that deals acid damage is an acid effect and thus has the acid keyword. ...?
Or is there an assumed 'generally' or 'should' in there - as in, "When we designed the PHB powers, we gave all the ones that dealt acid damage the acid keyword, but it cannot be stated with certainty that any time acid damage is delivered, the acid keyword is therefore attached to the power"?
Taking P55 at its word, we would know that a power that deals radiant damage is a radiant effect and thus has the radiant keyword, and so if Overwhelming Strike deals radiant damage thanks to ToL, then Overwhelming Strike is a radiant effect thanks to ToL, and thus has the radiant keyword thanks to ToL.
-Hyp.

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Rulebook featuring "high magic" options, including a host of new spells.