It seems obvious that it comes from the Indo-European root lewk. (But then, I'm not an etymologist, so there may be elements I am missing.)
This is the root of my idea:
Loki's association with Fenrir would seem to validate this (i.e. λύκος/lúkos is also cognate with this stem.) There is actually a very well constructed thesis on the relation of the root words for wolf, locust (i.e. "wolves of the air") and light in relation to Apollo titled "Apollo the Wolf God".
In addition to that, a relation can be drawn between Loki and Lucifer, the "Morning Star", as nemesis of the "Sky Father/Lord in Heaven". Further, Loki is an agent of Ragnarok, which can be related to the New Testament idea Armageddon.
There is a similar pre-Christian parallel to Prometheus, who stole fire. Both defied the Sky Father and were bound.
Finally, the inextricable relationship of Loki and Balder would seem to sugget such a meaning. The impetus for Loki's treachery is based on his jealousy toward Balder "the Bright". There is no indication that Loki's name has anything to do with darkness, so this is not a relationship of opposites in that regard. Further, much of Loki's stories have to do with cleverness, a modern meaning of "bright".
All of the relevant languages are part of the Indo-European family, and Norse Mythology has many parallels to Greek Mythology.