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An audience watches a laser light show during the SIB trade fair in Rimini, Italy in 2002.
Audience scanning (sometimes called “crowd scanning”) occurs when a laser beam is directed toward the people observing a laser show or display. Although this is necessary for many laser effects such as tunnels, it is potentially dangerous due to the potential for exposing the eyes of the audience to damaging levels of laser light.
Laser effects involving audience scanning are created by scanning the beam very rapidly across the audience, ensuring that the net exposure to any one eye is very small. Should the scanning mechanism fail, however, it is possible to expose people to laser light at levels that may produce eye injury.
Contents
1 Legality and regulation
2 Relatively few laser injury reports
3 Possible reasons for the lack of reported injuries
3.1 Injuries are not being noticed
3.2 Injuries are not attributed to laser exposure
3.3 Other mechanisms are reducing or preventing noticeable injuries
4 Audience scanning calculations
5 How to make audience scanning safer
6 References
7 External links
//
Legality and regulation
International legislation concerning the legality of audience scanning varies greatly. The biggest point of contention is the method of calculating the level of exposure actually received. 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. Audience scanning is not widely practiced in the United States; it is far more accepted in the United Kingdom, despite having been stopped for a period, and in the rest of Europe.
Relatively few laser injury reports
The lasers used for many laser displays have energy levels that can exceed the MPE within a few tens of microseconds. 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. Yet reported injuries from medical reports, and even anecdotal reports are rare.
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. As reported in a 1997 paper presented at the International Laser Safety Conference, the study found only five accidents (claimed injuries) and two incidents (potential injury). Accounting for an estimated 90% under-reporting factor, the ILSC paper estimated that there were roughly 70 injuries per decade a relatively small number considering the total number of concert-goers and disco patrons exposed to laser light, some night after night.
(Since 1997, there have been one or two reports of serious accidents involving pulsed lasers being used at discos. Pulsed lasers can be much more dangerous than the continuous-wave lasers used for audience-scanning displays. Because of the danger, they should never be used for audience scanning, or where there is a danger of the beam going into the audience.)
Since reports of laser shows substantially exceeding the MPE are so common, yet reported injuries are so infrequent, this leads to the question of “where are all the injuries?”.
Many safety experts are certain that the injuries are occurring, and are going unreported for several reasons. It is also a fact that the eye can often receive several thousand “damage spots” or lesions to the retina without it causing a significant problem to the subject’s visual acuity.[citation needed]
The consensus among many respected safety professionals[who?] is that the although the study conducted in the mid nineties had good intentions in trying to establish its goals, the methods in which the study was conducted were somewhat flawed, and could not give a proper indication as to how many injuries are occurring.[citation needed]
Possible reasons for the lack of reported injuries
Injuries are not being noticed
Affected viewers simply don’t notice any vision problem. The human vision system has ways of compensating for damaged areas, especially when this happens on the periphery. Often sophisticated tests are needed to map out the retina and determine areas with a loss of vision.
Injuries are not attributed to laser exposure
If vision loss is noticed, this may be put down to other sources instead. Persons affected may not realize that a laser exposure caused their visual problems.
Other mechanisms are reducing or preventing noticeable injuries
The 1997 ILSC paper presented some additional reasons why injuries are either not really happening, or are not being reported. Among the suggestions:
MPEs have a built-in safety factor. MPE…(and so on)
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