Audience scanning

Should the scanning mechanism fail, however, it is possible to expose people to laser light at levels that may produce eye injury.

The MPE (maximum permissible exposure) is essentially the same throughout the world, but some countries are far more conservative in their estimations of the amount of light received by the eye.

Measurement and calculation techniques both show that the beam durations that audience members are routinely subjected would indicate that the MPE is being exceeded, often by a significant factor.

For example, a 1996 study commissioned by a lasershow related company tried to find worldwide reports of audience scanning injuries at any time during the then-20 years of laser light shows.

The result will give the irradiance, MPE, Nominal Ocular Hazard Distance (NOHD), and other safety-related characteristics for a fixed beam at the closest point of audience access.

For simple, repeated scan patterns, it is possible to calculate the maximum possible exposure, by looking at the location (such as an edge) where the beam is moving slowest (longest dwell time).

[1] "A Risk Assessment Methodology for the Use of Lasers in the Entertainment Industry", PhD thesis of John O'Hagan of the U.K. Health Protection Agency.