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I've a couple of questions regarding stacking multiple area effect spells:

  1. Does Celestial Brilliance spell (BoED p94) stack with itself? That is, if two instances of this spell are cast and an evil outsider is within both areas of effect, does it take 4d6 points of damage or 2d6? Why? (there are plenty of spells like that, e.g. wall of fire, it's just Celestial Brilliance which is easy to stack)

  2. What if it was an emanation, instead of an unspecified area effect?

  3. What if it was a spread?

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As a DM, I would break out the most resounding "NO" I had in my bag of tricks, answers, but at first glance I can't find a rule that allows or disallows it either way. – dpatchery Jul 5 '11 at 14:35
I think the part that says "different strength spells only use the best version" covers it. – Cthos Jul 5 '11 at 14:38
@Cthos yep, definitely. Good find. – dpatchery Jul 5 '11 at 14:40
up vote 15 down vote accepted

They would not stack

It's covered by this sentence:

In most cases, modifiers to a given check or roll stack (combine for a cumulative effect) if they come from different sources and have different types (or no type at all), but do not stack if they have the same type or come from the same source (such as the same spell cast twice in succession). If the modifiers to a particular roll do not stack, only the best bonus and worst penalty applies. Dodge bonuses and circumstance bonuses however, do stack with one another unless otherwise specified.

Emphasis mine.

Edit: Note, that this is referring to Bonuses, but I believe the same applies to Damage as well, unless the spell says it stacks, it wouldn't stack.

Similar Reference in the Magic Section:

In cases when two or more identical spells are operating in the same area or on the same target, but at different strengths, only the best one applies.

Which I think covers the damage stacking aspect.


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@AceCalhoon - I edited with a more concrete reference. – Cthos Jul 5 '11 at 14:41
+1 The second quotation is what seals it. Note that the rule applies for all scenarios 1, 2 and 3 in the question. The type of area of effect has no influence on the stacking rules. – dpatchery Jul 5 '11 at 14:43
Thanks, your second quote is what I've overlooked. (being theoretical now) Still, since the damage is rolled anew each round, is it rolled twice and the larger applied? Or we should use Same Effect with Differing Results section rule here and apply only one instance of the spell? Or both spells have similar effects with similar (2d6) strength and, once again, only one of them applies? – Jeor Mattan Jul 5 '11 at 15:50
@Jeor I would say you would only roll it once. I've always read it as since they have similar effects only the stronger (pre calculation) applies. So you'd apply the "similar effect" rule before rolling. And since they're both 2d6, only 2d6 would ever get rolled. – Cthos Jul 5 '11 at 16:30

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