It would make sense thematically. I know her Lucent Singularity and Final Spark do. 
Edit: Other nerfs could also come if this is changed.
Edit 2: If this was made as a change and a compensation nerf was also included, she could become more utility oriented in the fact that she could provide vision to the team with her spells. Which I think fits her more thematically, again.
And obliterate Zed's W :D
"Banish the Shadows!"
tee hee lets buff lux even more guys nothing went wrong the last time we buffed an already strong champion
I personally would love it if her passive would grant vision, both thematically as well as being able to autoattack marked enemies as well as having the vision to aim her ult.
Light doesn't move at about 15mph, though.
When people try to use real world logic to balance a video game.
Sigh.
It would make alot sense if her passive gave vision, but thats actually a strong buff to her utillity, so it would need to come with compensation nerfs elsewhere on her kit as she currently has no room for straight buffs.
Maybe some just aren't bright enough?
Honestly there's probably a balance reason why they don't. But I'll admit it'd be interesting to see her do more things with light.
As long as this only applies to her damaging spells, then it sounds fine. Blind Qing someone in a bush should give you vision on them, it doesn't really change much since you're likely to drop an E on them anyway.
Lux is strong? Does that mean Viktor, Cassio, Syndra, and Aurelion are busted?
This sounds wonderful, and I'd totally support this. As you mentioned, not only does this fit Lux's theme perfectly, it also complements her support playstyle, and would more generally cement her niche as the most utility-oriented artillery mage out there. I'd be happy to see Prismatic Barrier provide vision on travel, since it often gets thrown onto whichever enemy Lux is attacking, despite it doing nothing, and it might be interesting to have Illumination itself live up to its name and reveal marked targets, though probably for less than 6 full seconds.
As others have mentioned, though, Lux isn't in too bad a spot right now, and she might need to be toned down elsewhere to accomodate this kind of change. Personally, I'd advocate toning down the damage on Lucent Singularity and/or Light Binding, and increasing Illumination's damage by the same amount, which would leave her ult combo unaffected, but would give her less poke in lane. Now that Light Binding roots for the same duration on both targets, it might be better if its duration scaled with rank, i.e. from 1 to 2 seconds, rather than 2 seconds at rank 1, which is pretty strong.
Riot, please!
(And True Sight on 
's R!)
only if standing in sion's shadow makes you nearsighted
lux does not need buffs
Makes sense to me.
Do it Rito!
Her E and Ulti do, gut her Q doesn't. IMO it should give vision of targets she snares.
Yeah they should, let's have her passive reveal enemies and compensate for this by increasing her ult cooldown.
Bring back Finales Fulken
Real life =/= video games. So in your logic Lux's spells should travel 299,792 kilometers per second since light travels 299,792 kilometers per second and it would fit her more thematically. I don't want her damage/cd/mana cost etc to be nerfed just for some vision. She's fine the way she is, and for those who are complaining about her damage, her damage is fine considering that all of her spells are skillshots.
ok but then her damage needs to be nerfed 50%
Worst Idea. Lux is perfectly balanced a buff even to her utility would be too much. Don't fix what isn't broken. It's not because it fits her theme that it should be a feature to the game. Wanna buff someone? Here try these guys
