I've been following a lot of the guides for Lux on here, but was finding that some of the items just weren't working for me. So, I decided to make my own little build on here.

A lot of Lux's potential for high damage and high kill count is based off of her ultimate, Finales Funkeln. So, optimizing your ability power and stacking cooldown reduction is important. Also, Lux can burn through mana really quickly, so getting those mana runes is important. Also, magic pen, duh! So I went with Greater Seal of Clarity for helping fix mana problems, Greater Mark of Insight for magic penetration, and Greater Glyph of Focus for cooldown reduction. As for the quints, I chose to stack Greater Quintessence of Potency for straight up ability power.

The masteries I chose made Lux have a little more health, a lot more mana regen, of course getting more gold and experience gain, and worked on ability power and magic pen, along with cooldown reduction. Early game she hits harder and I can usually keep from having to B for at least 10 to 15 minutes, allowing quick leveling and money gain wherever I happen to be laning. Late game, along with the runes I've chosen, the cooldowns and mana regen are so quick that I am able to do a lot of damage very quickly without having to go back because I run out of mana.

I used to be against getting a Doran's item first, but it is really helpful. So you start out with your Doran's, go back for an Amplifying Tome and some Health Pots, get your fiendish codex and speed boots, get that morello's then sorcerer's shoes, then its up to you which order to get your deathcap, void staff, rylai's and lich bane. It honestly depends on how the game is going. If you need health or if someone is tanky you either go for rylai's or void staff before you get your deathcap. Its at your discretion which of the last four items you feel most comfortable getting.

Clarity for mana. Flash because its awesome until it gets taken away.

In conclusion... this is just my way of playing Lux. I don't have much proof of it working, but its an easy build, you get amazing amounts of ability power, you get the max amount of cooldown reduction pretty quickly and you can pew pew that lazer all day long!