-Cactus KF36 @ 1/16th power aimed at background with a red gel
-triggerd via Cactus V4.
I've put up the set-up shot in the comments.
Update: The picture has been featured on the DIYphotography website in a post titled "21 Photographs And Lighting Setups For Every Occasion", yeeyyy !! Thank you very much you guys, you can check it out right here .
Update 2: The picture has been featured on Romina D's blog as part of her project "Mimic the master". She had great results with her set-up and i'm really happy to see how much interest people have taken into replicating this shot. Thanks a lot guys for all the support! Go check the original post here and the final shot with her set-up here