The 24-year-old will remain with the Os until January 2009, ending Ling's summer-long search for a left winger.
And the Orient manager expects the player to remain at Brisbane Road until the end of the season.
"He's a player who comes here with a good reputation. The reason he hasn't been playing for Luton this year is all to do with finances and nothing to do with ability," he said.
"He joins the club with a slight injury which he picked up in a reserve game against Colchester, and he's unlikely to be involved on Saturday, but as I said all along, it's not all about the August games but what follows in the season.
"He's here for five months and, if he produces what we know he's capable of, we hope to offer him something more permanent."