I just want to point out a few things on your guide which i find interesting.
THANK YOU for not focusing Lich bane first which is actually more likely to get you killed because of the stupid passive. Most people walk in there use a stupid auto attack that does 300 damage, then get focused and murdered in less than a second.

Also, what you said earlier:
"This is of particular use because the 0.5-1 seconds of time saved in comparison to attacking after detonation is 0.5-1 second less time for your opponent to react. This gives your harassment a higher chance to land, and less chance that your opponent can retaliate with a ranged spell of their own."

I don't understand why the timing is really that important unless they just block the auto attack with a shield but that would already blocked by the time they saw the Lucent singularity coming at them because the huge ball thing doesn't exactly fly super fast either.

My sister loves lux and so she played with your build and I must tell you... EXCELLENT! Go on ;)

Wow, nice guide. :D
I don't really like Mejai's Soulstealer, 'cause I always die too much with Lux -_- And I pick RoA, but the rest is almost the same as me :)
It's a really good guide, gj. ;]