One other, slightly related question that has just occurred to me - can trolls be illuminated? On one hand, it seems like it would have to be possible, and certainly Arkat was an illuminate who became a troll, presumably without losing that state of illumination.
But on the other hand, it certainly doesn't sound right, though that might be because trolls and anything with "light" in it don't go well.
Do we have any examples of illuminated trolls, other than Arkat?