I think your pretty much out of luck on this one. Definitely do your research into this guy and his light as well. Like mention above, you never know if he actually came up with this before you. You wouldn't want to make a big stink to find out he did it first.
I'm sure you could hear an endless amount of stories on this board, it happens to everyone, myself included. Its the nature of the business. I know it sucks to hear but you just got to suck it up and move on. Be proud of the fact that side by side, your design blows his away! You are just going to have to do a better marketing job now if you want the upper hand.
I also feel that its not a rip-off but used as inspiration. To me, he took your contemporary style and turned it into a much more industrial looking fixture. I don't think that a consumer would consider one over the other, they belong in two completely different environments in my opinion.
And on a side note, that Dark website has got to be one of the most annoying websites I have even been too!!
same sort of deal on a much larger scale..LG using the iphone menu as "inspiration" if you will...
Im sure they weren't happy either:(