Lux can EASILY carry a team fight, if there all bundled up, e + ulti, is easily half of everyones hp, add an annie, fiddle or kennen, etc. and youve won a team fight in under 4seconds? ive lost maybe lost 10 or so games, and won atleast 60+ while playing lux, i carry most games.
with my post earlier, i didnt include my build.
i start with regrowth + 1hp pot (mana seals take care of my mana), i focus on last hitting mostly.
first recall regrowth into philo, i normally get first blood with snare, so i rush mejais, and boots, and a ward if i have the gold, its about 2k before i recall, (boots 1 not 2)
after that i rush rabadons because mejai's building + rabandons is easily 300ap, i finish boots when i can (CDR boots), void staff next for mpen, rylais, and finally i build either hourglass if a xin or another melee carry ignores the team fight and comes right for me, or i just build morellos for the CDR.
get blue, ulti every 24seconds, run CV for easier snipes, get early kills with ulti. lane with someone with a stun or slow, any tank is fine, tanks do alot of damage at low levels, stuns + snares + slows is gg for any lane, lux normally gets fed lane phase, you become useless mid game, just finish people off with ultis, end game you carry. Have fun!
edit: always lane your ward, save flash for team fights, that 75g is never wasted. you shouldnt ever die as lux. her range is amazing.