It seems the outcry here is largely that this name sounds "too cool" for Lux, who is a softer-style character (though to this, Prismatic Barrier and Lucent Singularity are pretty "epic fantasy" names as well).
Take Lux's explanation of a "Double Rainbow": Well, a "double rainbow" is a phenomenon of optics that displays a spectrum of light due to the sun shining on droplets of moisture in the atmosphere. Does that explain it?"
Lux's explanation of a double rainbow reveals a lot about her character in my opinion.
Prismatic Barrier and Lucent Singularity sound like names she came up with on her own without premeditation. Complicated. Almost unnecessary synonyms for much simpler terms.
"Finales Funkeln" always fit for me. I felt as if she wanted you to inquire as to what she meant by such a phrase. She wants to share her knowledge.
"Infinite Light" sounds too simple. A Lux who named one of her own fantastical skills "Infinite Light" would probably administer a much more bland explanation of rainbows.
It just doesn't fit her personality.
I realize "Light Binding" is ALSO a simple skill name. To take this into consideration is to acknowledge as well that "Light" would be used for two skill names. I don't think Lux is that redundant. She seems like someone with a whole lot of synonyms - many that you would never use - up her sleeves.