Philippa Boyen's lyrics for the second half were meant to read "And the white light/Of forever fills the air" but that's not really what that Sindarin says...
 Also wondering whether there's some spelling differences in there, e.g. is naed meant to be naid (as in "Ah my love, no things...") and is trehil meant to be tre- + síla so it means "and shine (white) the pure white light forever through my air", with the nuance of 'shining to completion'.
Edit. Well unless it's meant to be 'anin' instead of 'nin' in which case it's 'to me' and makes rather more sense than 'my air' which is somewhat nonsensical.

There have been typos in the booklets before; I would have expected 'lân for 'ân, for example.

At any rate, naedhathog looks like (to me) a fut. 2nd. p. verb "Oh, my love, you will not naedha my heart"

+Matt Dinse a cognate of Qenya naitya "put to shame, abuse"? Or perhaps a causative variant of naina- " lament"?

Heh, I hadn't actually read it as one word (and searching for the lyrics online show it as two words in some places too, just to confuse matters :( )

I think *naedha- comes from the root SNAG "wound, gnash", cf. Q nahta- "hurt, injure, wound" (cf. PE/19:91).

So the first sentence means "Oh, my love, you will not hurt my heart", though hûn should have been lenited to chûn.

I guess the second sentence literally means "And shines through the white light (of) eternity through my air", if the correct spelling is "A trehil i 'alad 'lân uir trî 'wilith nín".

Thanks so much, everyone! :)