The "Latin for light" idea is a bit scrambled ... I'd explain it this way.
In Latin, light = lux. This gives us names like
Lucy.
In Greek,
Helen is linked to
Hellen = fair-haired - how accurately, I don't know, but it's a common perception. People might well decide to name their twins
Helen and
Lucy so their names could "mean the same"; from that kind of idea to identifying Elana with
Helen and
Helen with
Lucy would be a small step indeed for some naming sites.