I've played both as Lux already has low cooldowns like said before, you don't need to reduce them any more. It just didn't seem like my personal style, especially since I don't go for kills often.

Again, it's simply what kind of situation you're in that determines your item build. CDR is simply what I most commonly use and it works for me since I don't purposely try to go for kills, but for assisting my teammates in getting their kills. It's mildly frustrating to hear them go "Snare them!" and Light Binding isn't available and on cooldown. Since I main Sona, I mainly wanted to go for more of a mid-damaging support, rather than just plain damage. I don't like to solo queue very often. When I do, I often end up playing other characters.

Sometimes I switch out my CDR items in the middle of the match for more AP or Magic Penetration, but again it's situational.

I thought I'd suggest a few other ways for you to try playing Lux with and to help you experience others ways there are to play Lux. With knew experiements, see how it changes your build. =] I've used Lux as my main champ since release, and I have tried many builds, including ones like this. I found that attacking less often but more damaging works excellent. Try working with

AP + Mana Regeneration - OR - Ap +Magic Penetration.