Hello. It's my first guide and i have bad English so... don't expect that much but i will try to explain as much as i can. You're teammates might rage in this build because you need kills(not really..) like brand supports for the stacks. But if all goes well, you're teammates will shut up and play. This build will also give enemy champions a hard time laning with you. Read more if you're interested on how it works.

***
This guide is for low-avg elo or higher , since Lux is easy to use.
Requirements:
Needs to learn how to use Q properly and combo( E>Q>R or Q>E>R).
that's it.

***
Example of a Game that can be favorable for you. (Might be confusing.. Sorry.)

This build will be some more of an AP mid than a support. Example's why this build is good for low-avg elo. Your enemy team has SONA as their support while you're lux. In mid-game(10-20 min ?) , your enemy consist of 2 bruiser(who has low magic resist items), 1 adc( no magic resist at all or has the boots with magic resist), 1 support (that only heals and speed things up (?,her e?)and 1 tank. While you guys have 2 AP , 1 bruiser , 1 support jungler/another bruiser/tank and adc. In mid-game you guys can just out push the enemy side by just going om(only mid) because of having 2 AP ( mid/you). Having Liandry's and Sorc's Shoes will already be enough to eliminate anyone with no magic resist in mid-game. I prefer letting them initiate since you have good cc skills to counter it.

***
IMPORTANT NOTES:

Get the kills in laning phase to easily stack glory. This is OPTIONAL. When you're lvl 6, even with no stacks in THE DARK SEAL RING, you can easily 1 hit combo your enemy adc!.

Get MAGIC PENETRATION ITEM'S as fast as you can. More earlier of the game the better, since enemy champions will still not have MAGIC RESIST.

USE E then Q to have a better chance of snaring champions with you're lane with or if you see
a opening use Q but engaging team fights when you initiate using E will be easier.
*Technique for people who knows the basics. Use Auto attack then Q, to easily proc passive.
This technique is just optional, doesn't work every time. hahaha..


This build is like BRAND SUPPORT BUILD. but better or maybe, since brand has higher AP but he's combo is quite hard for a new people. But this build is like it so.. you can build it like brand but replace spellthief with ancient coin.

Don't mind their support just aim the enemy ADC. You can mind their support if isn't a tankyish type or is likely AP but karma!

You will literally carry the game with this build :)

***
(QUESTIONS AND ANSWERS), things to be explain and such
So probably you're thinking why Ancient coin ?, Why Dark Seal ?, Why Barrier?, and so on.

Item Guide:

Why BARRIER, Lux has a SLOW and a STUN/SNARE. That's why exhaust and ignite isn't really needed. With barrier, you can force team fights. People will probably target lux since she's really squishy than her ADC but with barrier you can hog all of their attention and don't die in the next 5 secs. This means that you're adc will have more space to easily free hit their adc and win team fights in laning phase.

ANCIENT COIN will give you gold without forcing to use your MANA and that' really good for lux since her cooldown in early game is really bad. Using your skills efficiently/(the right possible time) will really help your adc a lot.

THE DARK SEAL RING ? why buy it ?. Simple, this item gives AP( 10 stacks = 45 AP). I know 10 stacks is hard to get. NOPE or not really, Since BARRIER will help you a lot in forcing team fights in early(5-10 min) game. This will help you get stacks and getting more stacks means you can have HIGHER AP to do in a single combo. Getting 10 stacks in 13-15 min, is a big threat to your enemy because they're weren't expecting your damage will be that high!

Why not Upgrade it to MEJAI'S SOULSTEALER? to risky. Compared to DARK SEAL RING -4 glory per death, its x2.5(-10) than its its originally was and it cost 1050 gold more than the ring for +100 MANA and +5 AP is really bad. REMEMBER YOU'RE A SUPPORT, support are efficient to gold. If you're skilled enough or want to try it, sure why not ? but remember 1050 is at least near the cost of Sightstone and boots.


Have more questions just comment below. I will try my best to answer it. Please no hate if you lose . I'm still experimenting this build.