I agree that this one is a bit more 'peaceful' than what we are going for, but we probably don't want to make it look like Fëanor is lying there writhing in pain before he burns up, either. So, that happy balance between natural death and very unnatural death .
In The Dark Crystal, the ending scene involves the Skeksis merging with the Mystics. I didn't find a good uninterrupted clip of that scene, but the visuals at least are here (at 3:41):
I think we can probably do better than 1980s special effects, but I bring this up because the Skeksis, at least, are quite unhappy about this event. There is likely a way to convey that in Fëanor's death without resorting to making it look like torture.
Yeah, so far the closest I can find to what I want is this clip, and it's still a little too horror/gore for what we want to use. (25 seconds in)
It has the welling up light (reddish, not white), it has the pain, it has the bursting into flames, and it has the turning to dust/ash after. But....yeah, not what we want to do. Certainly, we don't want Fëanor's eyes to catch fire. I'd rather see light there, and fire elsewhere.