Abyssal scepter is pretty much useless on lux... she shouldnt be close enough for the debuff to be effective. yes, it does give AP as well as MR but if you need MR banshee's veil or Quick-sliver would be better for that. If you wanted more AP and a little MR Lich Bane gives 30 MR plus an awesome proc on Lux because her passive also deals bonus damage after a spell. I would highly recommended those items over abyssal scepter because a good Lux wants to use her range to her advantage instead of being in the middle of everything like singed or amumu. The rest of the build looks fine however i would not play her as a AP Carry + support because of the fact that there should be a true support on the team to do. I like the CV idea because it frees up a summoner on the support. I also think exhaust would be nice to catch out of position champs when your stun is down. I would probably go with ignite myself.