It certainly looks like a grating effect anyway, but I can't figure out how exactly it's done. I would bloody well like to know though!
Have a look at this (and the video response):
http://uk.youtube.com/watch?v=pnXQBEqgeos
It's apparently this baby:
http://www.kam.co.uk/products/lighting/STARCLUSTER.htm
I would love to know what gratings in what configuration you would have to use to get that effect though.