For Lux, how about making E overloaded?
Lux's supposed to be this high-impact, high-cooldown, long-range burst mage, right? Abilities are cool when they have a lot of depth. Instead of lowering E's cooldown, projectile speed, width, or other statistics that don't "feel good" for the Lux player, why not just increase its cooldown and other effects?
Lucent Singularity -> Cooldown UP -> Sight Width UP -> Damage UP vs live the faster you pop it -> Damage DOWN vs live the longer it's held -> Slow UP
If its cooldown were doubled, for example... but it were made as viable of a sight/scouting tool as it is a slow field it'd feel pretty good for the Lux player. They could then think... "Hmm... should I throw this thing out to see the dragon pit? If I do, I might not have this spell to protect myself and/or my teammates. I'll also lose a bunch of burst power for 20 seconds. For a "light mage", Lux seems to have less effective vision tools than Kalista.