Once her tongue slid around in a dance, she gently stuck the the "明かりに反射した光" (spit?) onto her hand using her slim fingers.
(normally there isn't anything that hard to read in a H-scene, but if you havn't realized the context is a BJ, with the speaker asking her to used her hands along with her mouth with spit as lubricant :X)
can 明かりに be an adverb, as if 明かり is a na-adj? Is 明かりに反射した光 gibberish regardless?
Is the meaning between 指先を光が手に貼りついた and 指先が光を手に貼りついた interchangeable?