We use Zones in hardware and software that reduce the power below the "zero" or horizon line. Scan Failure Safeguards (Required in the US) Wickedly expensive hardware, we own calibrated laser power meters, oscilloscopes, fast photodiodes set up to mimic the eye, years of training, legal certification, have a laser safety officer check our work etc. We don't share the hard won information on how to construct safe audience scanning frames and animations with just anyone who asks. Why? Because of the risk that some idiot will argue that info should be "free" and then publish a simplified "APP" for a cell phone, distribute it, and the math will end up wrong. Then another idiot will publish the frames, some one will do a show without meeting all the required pre-existing conditions, and some one will get blinded.
Also we stand down range and view our own effects. This tends to make one make sure we have done it right. This is so we can sleep at night, as lasers are dangerous.
Hint: Increasing the repetition rate of the scan actually increases the exposure time.
There is an internationally approved concept called "Maximum Permissible Exposure" and we stay below the cumulative MPE for an eight hour day.
Requires massive amounts of math, and in the US is quite illegal, without a document allowing you to break the 2 and 3 meter rules.
2 Meters horizontal Separation and 3 meters vertical Separation from the highest accessible audience point is the norm for a conventional laser show. Very few people make it to the level where they are allowed to do that in the US. I've taken the classes over the years, been in the audience many times, can do it, but choose not to do it.
Every single part of every single effect gets checked and measured on a second by second basis when your doing it right, and for a typical four minute song, that is a LOT of work.
Now you know a tiny bit. Don't try it, because even at the MPE, it's more then bright enough that it hurts. We have to dial it down even further.
If your asking the question, or reading this to find out how to do it, and have not taken the classes offered by a few consultants, and passed the LSO exam, you don't have a clue and should NOT try it.
Massive amounts of quality control procedures are used, before, during, and after.
The example once explained to me by a Di*ney chief safety officer was this: You have an experienced Brain Surgeon in your audience. Even though you didn't harm them, and can probably be reasonably sure you did not, after doing all the math and quality control checks, he/she files a claim anyways. Can you really afford to pay 450,000$ a year in legal payments plus punitive and cumulative damages for the rest of her/his career? In other words, if you screw up, your basically bankrupt for the rest of your life.
The scan failure safeguard is required to act 100% of the time in 200 nanoseconds or less, that is NOT easy to engineer. Did I mention the 3200$ special laser power meter for pulsed exposures?
nough said.
Steve
