Rawr is a good tool for answering these kind of questions, or if you don't want to install Rawr, at least search the forum. A quick search for "lightweave" on the Mage forum gets quite a lot of answers.
This may have been answered in this thread, maybe even a couple times so please do forgive me because I failed to notice it.
I was curious though if the lightweave embroider to cloak is a better choice than the + Haste for overall dps.
Im currently 20/51/0 raid spec and the lightweave just really does not seem to proc all that often.