The song is about a guy who is apparently with a girl he doesn't feel love toward and is probably just using her for sex.
Then he notices this girl (who ionizes and atomizes), falls in love with her blah blah and notices how empty his relationship is. Fluorescent lights are just a part of real light and that's what his relationship is, part of real love, etc.
"she ionizes and atomizes then turns into sunlight"...."the real lights will make you heavy but never really empty flourescent light will always equal empty" hes saying shes the real thing, shes the sunlight and everything else is the flourescent light, empty.