When you scan an audience, their eye safety is in your hands. In addition, your reputation could be on the line.
Just one claim of injury could be devastating to your business. Remember, it is up to you to prove that you were at safe, known levels. Video recording, as mentioned below, also provides evidence of the laser's locations and exposure during the show.
• If you are unsure about how to create a safe show, or how to measure the beam power -- DON'T DO AUDIENCE SCANNING. Get the information you need before you expose the audience.
• If you are doing audience scanning shows, the information below gives some tips and suggestions. (For general information on how to measure the beam power, and on the MPE levels, see the page How to do safe audience scanning.)
Irradiance measurements to be required for ILDA Awards
Beginning with the 2017 ILDA Awards, all entries with human exposure must include contemporaneous measurements or calculations of the lasers’ irradiance at the point of closest human contact. “Contemporaneous” means that the measuring or calculating was done before the laser show started. This can help ensure that Awards entries are done at a known, safe and legal irradiance level.
Continuous scanning shows MUST be well-designed so that the beam is constantly moving. There should never be just a "dot" of light, or a few dots, in the audience. If you are shrinking a shape into a point, fade the beam out during the shrink, so that it is off by the time it becomes a point.
For RGB (white-light) projectors, if you put a white beam into the audience, they are getting the maximum power: full red, green and blue. But if you change to a green-only beam, now the power is reduced because there is no red or blue in the beam.
Thus, if you are scanning smaller shapes where the light is more concentrated, use a single color for these instead of white.
This page discusses power meters in more depth. Be sure yours is appropriate for the power ranges you'll be working with. Generally, this is from around 2.5 mW/cm2 when doing MPE measurements, up to multiple watts when measuring your laser output directly.
Also, be sure you know how to operate and correctly interpret the meter.
ILDA recommends that all audience-scanning projectors have working scan-fail devices. Usually these are built into a scanner amplifier. If the scan-fail circuit detects that the beam has stopped moving, it will blank the beam or otherwise stop it from being emitted.
An ideal scan fail device should trigger in 1 millisecond. Many devices are in the 20 millisecond range. This is OK, and is much better than nothing.
Be sure you know the scan fail device's limitations in special cases, such as where the laser is scanning rapidly between two dots. The scanner has not stopped, but this can be unsafe -- each dot has 1/2 the total laser power. An ideal scan fail device can distinguish this and blank it out.
The best way to reduce a beam's irradiance is to enlarge it. This is done with simple lenses. You should carry a set with you to shows. That way, if you need to change the beam's divergence, you can select a lens with an appropriate power.
Of course, you need to have a way to fix the lenses to the front of your projector. Make a mount in your shop beforehand. Or purchase a mount and lenses; at least one laser show supply company sells these.
Audience scanning shows are regulated in many countries, states/provinces and localities. See this page for a list of countries.
In the United States, a reviewed and approved "variance" from the Food and Drug Administration is required in order to do any laser show over 5 mW. Shows with audience scanning have additional requirements in the variance. No one in the U.S. should do an audience scanning show without an approved variance specifically allowing the audience scanning techniques and procedures. More information on U.S. laws is here.
Audience scanning is under increased scrutiny. There were incidents in 2008 and 2009 where injuries were claimed to be caused from laser shows. Also, under new U.K. laws, if someone states they were injured by a laser, the burden of proof is on the laser show operator to prove they were using safe practices and light levels.
For this reason, you need to be proactive. Assume that someone in the audience might claim an injury. Keep video and other records to help prove that you operated safely and responsibly. This would have been very helpful in the 2009 Belgian incident, to quickly absolve the laser show operator (the injuries were caused by laser pointer misuse in the audience).
Know and follow safe practices
You should already know and follow the basic principles of laser show safety. Especially, NEVER scan audiences with pulsed lasers such as YAG or copper-vapor.
Measure and record your irradiance, before every show setup
A power meter should be a standard part of your show kit, just like a laser and a projector. ILDA believes it is essential to accurately measure the audience exposure at the point of closest access. Do this before every show setup, and record this data. You may wish to videotape this process, or be sure that an independent person such as the producer or venue manager witnesses the measurements being done.
Videotape every show (ideally, every projector)
ILDA also strongly recommends that you videotape EVERY audience scanning show. At the very least, have one camera or webcam continuously recording the laser part of the show. Even better, use one camera or webcam for each projector. Mount it on the front of the projector so it sees exactly what the laser sees. Keep the recordings for at least 1-2 months, since sometimes injury claims are made days or weeks after the event.
ILDA believes that all audience scanning shows should be continuously supervised. The operator needs to see the scanned portion of the audience directly, or be in contact with audience observers.
This helps if the audience becomes unruly, such as floating reflective Mylar balloons into the beam path. This also helps if the operator sees laser pointers being misused by audience members. He or she can try to stop this, or can record the use via cellphone or camcorder, to help in case injuries are later claimed. (See above for a discussion about using video cameras throughout the show.)
Watch out for expensive cameras and video projectors
In addition to the audience's eyes, you should watch out for potential damage to cameras and video projectors. You need to be especially careful not to hit expensive, professional-level equipment often found in venues where laser shows occur. A single hit from a 50 mW beam can ruin the most costly part of the projector, the sensor/lens assembly.
Because it is nearly impossible to avoid cameras and camcorders brought in by the audience, ILDA considers that laser producers should not be responsible for damage to audience members' equipment -- especially if the show is at or below the MPE for eye exposure.
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Photo credits: Top, 2015 ILDA Awards, photo by 3rd Dimension EvenTech. 2014 Award winners, photo by Patrick Murphy, ILDA