Audience Scanning - ILDA Audience Scanning Guidelines

ILDA Audience Scanning Guidelines

In November 1998, a panel of safety experts and laser operators, convened by the International Laser Display Association, issued a joint statement regarding audience scanning. It included these guidelines and a cautionary statement.

"No system or test can absolutely guarantee eye safety when deliberately scanning the audience. You should use accepted instruments and practices to check the questionable parts of your show. The following tips are general ways to make your show safer through good design practices, and if accepted instruments are not available at your show site."

• "Do not scan with pulsed lasers (e.g., metal vapor, pulsed YAG, pulsed solid-state). They are inherently hazardous due to the power of each pulse. It requires exacting calculations to even consider scanning an audience with pulsed lasers. Because of the great potential danger, use continuous wave lasers (e.g., he-ne, argon, krypton, diodes, cw solid-state / DPSS) only."
• "Increase divergence. For ranges of less than about 30 meters (100 ft), using a lens to increase divergence can allow for visually effective power levels while maintaining controllable irradiance levels. A bright, fuzzy beam is far safer (and more visually effective) than a dim, tight beam with the same irradiance."
• "Don't use a single beam. You should never aim a single beam into the audience. In general, if a single beam is safe, then any scanned effects such as cones and fans will spread the light out, and be too dim to be effective."
• "Move the projected effects. When projecting a fan or tunnel, move the effect through the audience. This reduces the multiple pulse accumulation."
• "Don't rely on faster scanning. In general, you will not increase safety by scanning faster. Although the beam spends less time in the eye, there are more crossings of the eye, and thus the total light energy delivered remains about the same."
• "Attenuate power with size. The smaller the projected effect, the greater the concentration of energy. Any effect that grows from a point, or shrinks to a point should have a proportional fade in/ fade out."
• "Limit anchor (dwell) points. Anchor points reduce beam velocity and increase exposure. Where possible, use blanking to emphasize beams, rather than anchor points."
• "Use a scan fail interlock of some sort. Chances of a still beam from a laser entering someone's eye are small, but consider the consequences!"
• "Program "no-exposure" periods in the show. Allow time for the eyes to recover by parking effects outside of the audience area. A good "no-exposure" time is 10 seconds or longer."
• "Measure the irradiance. Typical shows should not exceed 10 milliwatts per centimeter squared, or 100 watts per meter squared. You need to know what you are delivering to the audience."
• "Quick test for aversion response. Note: The following tip is only for use when you believe your show is safe by using the above tips AND you are aware you could damage your eyes if your show is not safe. Use your computer or PCAOM controls to set the laser output to all green or all white. Run the show while standing at the closest audience access point. As the laser crosses your eyes, evaluate the brightness. If you have a desire to avert your eyes, you are probably approaching or exceeding the internationally agreed safety levels (MPE)."
• "Use Attenuation Maps. In some laser software, it is possible to set up attenuation maps, which allow the laser operator to program a zone where the audience will be. If a laser effect falls into this zone, the software will dim or completely cut off the laser to avoid excess exposure."
• "Respect the audience. Not everyone enjoys bright lights in their eyes. Remember that they trust you to ensure their safety."