We've all seen recorded laser beamshows where the beams fan out in a circle in all directions away from the scan head. Then various forms (walls of light, star-like beam paterns, etc) move back and fourth, up and down, all in time to the driving beat. It looks very cool...
Now, how the hell are you going to do such a show while still adhering to the CDRH rules that specify all beams must be 3 meters off the floor at the highest point in the audience, and must have a horizontal separation of 2 meters on either side of where the audience can stand (or sit).
This means that there is a central cone (well, a rectangle actually) where you MUST NOT have any beams. Yet in order to accomplish the effects listed above, the beams *must* swoop through this audience area.
I thought audience scanning was not permitted? (Or, more correctly, that the calculations required to prove you're under the MPE limit for every point of every frame become so tedious and involved that no one is willing to go to the trouble to try and get an audience scanning show certified, especially with the various interpretations of what, exactly, constitutes the MPE...)
So what gives? Are all these shows we've seen on video actually outlaw shows? Or maybe just shows that are only open to private groups, where the CDRH has no juristiction? (They have no juristiction if there is no "commerce" involved, either directly or indirectly, with the presentation of the show.)
This has me confused, because one of the wining shows in an ILDA competition a few years ago seemed to violate the rules for audience scanning. And it seems odd that someone would go to the trouble to create such a detailed show and submit it for the competition knowing that it could not be used commercially.
So, what is the missing piece of this puzzle?