Scanning Audiences at Laser Shows Theory and Practice
- Slides: 71
Scanning Audiences at Laser Shows: Theory and Practice. . . and a Proposal Patrick Murphy, ILDA Executive Director Greg Makhov, ILDA Safety Committee Chair
What is Audience Scanning?
“Creating beautiful mid-air beam patterns which surround and envelop the audience, for entertainment and display purposes”
International Laser Display Association
3 important points • Scans are not intended to enter the eye – An undesired consequence • “Audience scanning” means deliberate exposure only – Does NOT include accidental exposures from non-audience scanning shows – Visible, continuous-wave lasers only – Never use pulsed lasers (ex: Q-switched) – Only CW lasers discussed in this paper International Laser Display Association
Audience scanning is widespread outside the United States 50, 000 spectators 2006 Asian Games Khalifa Stadium Doha, Qatar
How many people have been exposed?
Conservative estimate • Number of people exposed to direct laser beams: – 100 clubs with 100 people nightly: 10, 000/day – 3, 650, 000 people experience this yearly – 109, 500, 000 people over the past 30 years • Number of exposures per show: – Beam crosses the eye an average of 20 times per show – Typical 5 pulses each crossing – 100 pulses per show International Laser Display Association
109, 500, 000 people x 100 pulses per show = 10, 950, 000 pulses over 30 years
What laser power have these 110 million people been exposed to?
Typical raw laser power • 500 milliwatts to 5 watts raw power (at laser, before projector optics and scanner) • As much as 20 watts raw power for larger shows International Laser Display Association
What is the irradiance at the audience? • Exact irradiance unknown • Estimates from laser show and safety experts – Greg Makhov, John O’Hagan, James Stewart • Most shows are above the MPE at the point of closest audience access • Many shows are far above the MPE – 10, 50, 100. . . even 300 times the MPE International Laser Display Association
Typical show • 3 watt laser • After optics and scanners, about 1 watt output toward audience • 1 milliradian divergence • Closest audience access 25 meters International Laser Display Association
Typical show, cont. • Static irradiance: 162 μW/cm 2 – (65 x the static MPE) • Well-designed scanning effects, no static beams • Reduced hazard 4 x – Single pulse MPE applies; 16 x single pulse MPE • Performers located closer, at 10 meters – 75 times the single pulse MPE International Laser Display Association
Where are the injuries from 11 billion pulses, most over the MPE?
“Close to zero” injuries • 1996 study by independent research firm – Presented at ILSC 1997 – Looked worldwide – Found 5 reported accidents over 20 years – Article notes “there may be underreporting” • If 9 out of 10 injuries are not reported, this is 25 injuries per decade (2. 5 per year) "Is Deliberate Audience Scanning Unsafe? ", Patrick Murphy, Pangolin Laser Systems Proceedings of the 1997 International Laser Safety Conference, Vol. 3, pp. 493 -502.
“Close to zero” injuries • Google Scholar – 2007 article on injuries at a show caused by a pulsed YAG laser • “To our knowledge, only one case of eye injury during a laser show has been reported previously. ” • “The lesions resolved within 3 months” Retinal Laser Injury During A Laser Show Shneck, Marina MD; Levy, Jaime MD; Klemperer, Itamar MD; Lifshitz, Tova MD Department of Ophthalmology, Soroka University Medical Center, Ben-Gurion University of the Negev Retinal Cases & Brief Reports: Volume 1(3) Summer 2007, pp 178 -181
“Close to zero” injuries • Google search – No reports found of incidents of audience members at shows with CW lasers – Not even informal complaints on blogs or forums International Laser Display Association
“Close to zero” injuries • Rockwell Laser Industries database of over 1600 incident cases – Only two cases involving deliberate audience scanning with CW lasers: • One case of “eye irritation” following a laser show, 1980 • One case of retinal scotoma produced while watching a laser show (beam hit into eye), 1997 International Laser Display Association
Worst case findings • Based on 1996 study finding 5 incidents over 20 years • 2. 5 reported injuries per decade • Estimating 90% underreporting: • 25 estimated injuries per decade, worldwide
How does this compare? U. S. amusement park rides Lasers • 2. 5 reported injuries per decade • Due to underreporting, could be 25 injuries per decade • Worldwide • 72, 000 reported injuries per decade • 44 deaths • Just one country International Laser Display Association
Important caveats • Not saying there aren’t changes to retina – It is unknown whether shows cause laboratory -detectable changes • Not saying the MPEs are wrong – We believe in and support the MPE levels International Laser Display Association
Our conclusion • Are saying that, after 30 years and 11 billion pulses, most over the MPE, there are essentially no complaints, injury claims, proven injuries, lawsuits, etc. from audience members • If there were, these shows would not be occurring – Clients were very skittish after press reports of July 2008 injuries caused by pulsed laser International Laser Display Association
Why are there essentially no reported injuries?
Reasons for essentially no injuries • MPEs have a built-in safety factor – Does not explain shows which are well over 10 times the MPE International Laser Display Association
Reasons for essentially no injuries • Lasers are relatively far from audience members – Gives time for beam to diverge • Audience is not always looking at the laser beams • Audience rarely focuses vision directly on the laser projector output (scanners) – Taking in entire scene International Laser Display Association
Reasons for essentially no injuries • Multiple pulses are safer than previously thought – Effect of multiple pulses not n-1/4 – See papers presented earlier at ILSC 2009 International Laser Display Association
Reasons for essentially no injuries • Pupil is smaller than 7 mm – Laser shows are usually presented with stage lights, etc. , so 5 mm is more realistic – At 5 mm: • 50% less light enters the eye • Pulse width is decreased by 30% International Laser Display Association
Reasons for essentially no injuries • 0. 25 second aversion response prevents serious damage from scanning failure • Small likelihood of hitting a pupil – Randomly positioned static beam has a 1/25, 000 chance of being on a pupil International Laser Display Association
Reasons for essentially no injuries • Avoidance response before beam crosses the eye – Move head – Look down or to the side – Blink or close eyes – View show while blocking beam emission point • Put up a hand in front of the projector output • Stay behind the head of the person in front of them International Laser Display Association
Reasons for essentially no injuries • Audience is spread out – Those closest to the laser receive the maximum exposure – Those farther back have a lower exposure, due to: • Increased divergence • Increased linear velocity of the scanned beam International Laser Display Association
Is it possible to create shows which are below the MPE?
Before: Very hard to measure exposure • Requires a detector watching the entire show • Only measures that one spot • To calculate additional locations, requires re-running entire show • Practically impossible to determine maximum exposure International Laser Display Association
Analyze scan characteristics. . . • Angular velocity of scanners – From 10 radians/sec to 100 radians/sec • Distance from projector to audience – From 1 meter to 10, 000 meters • Angular velocity * distance = linear velocity – From 10 meters/sec to 10, 000 meters/sec • Assume 1 mrad divergence (tight for a laser projector) • Beam diameter/linear velocity = pulse duration – From 2 milliseconds to 10 microseconds • Within range of Thermal MPE for 10 sec to 18 μsec – MPE for pulse is therefore 1. 8 x t 3/4 x 10 -3 J/cm 2 International Laser Display Association
. . . compare to MPEs. . . Exposure time MPE Notes Time compared to aversion response 1. 0 second 1. 8 m. W/cm 2 Aversion response protects against this exposure 0. 25 second 2. 5 m. W/cm 2 Longest exposure needed to be considered 0. 01 second 5. 6 m. W/cm 2 0. 001 second 10 m. W/cm 2 Typical slow scanning speed 4 x 18 microseconds 27 m. W/cm 2 Typical fast scanning speed 10 x 1 x 2. 2 x International Laser Display Association
. . . express scanning factor as a multiple of the static beam • Conclusion: Scanning the beam allows an increase of 4 times to 10 times the exposure, compared with a static beam. International Laser Display Association
Easy, safe measurement technique • Show measurement is vastly simplified: – Put out a static beam – Measure at point of closest audience access – Adjust power and/or divergence so the irradiance is 10 m. W/cm 2 (this is the MPE for a 1 msec exposure) • Requires a show with smooth, constantly moving scans • Recommended to use scan-fail safeguard or similar velocity-monitoring circuit International Laser Display Association
Problem: MPE-level shows are not impressive
MPE shows are dim & fuzzy • Shows done at the MPE are – Low power: Dim – High divergence: Fat, fuzzy beams – Require almost total darkness to be effective • Similar to turning down the volume at a disco or rock concert, to background listening levels International Laser Display Association
No longer an impressive show • Forcing MPE-only shows would be unacceptable to many clients and laser show producers – For 30 years, they’ve presented shows that are 10, 50, 100 times the MPE, with no injury reports – Want shows to be visually impressive, not wimpy International Laser Display Association
Solution lies in risk analysis and management
Risks in everyday life • People accept risk in their everyday life (driving to work) and in their leisure activities – Playing sports – Going hiking – Riding bicycles • These activities can and do cause injuries – Cuts (leaving visible scars) – Bruises – Broken bones International Laser Display Association
Injuries and life • Minor injuries (cuts, scrapes, bruises) are an unfortunate but inescapable consequence of leading an active, interesting life • NOT saying it is OK to cause injuries – Should minimize or eliminate if possible • But people routinely choose to participate in activities which eventually will lead to a cut, scrape, bruise (or worse) International Laser Display Association
Risk acceptance • People make individual risk/reward calculations, based on factors including. . . –. . . enjoyment of the activity –. . . chance of injury (bowling vs. tackle football) • People manage their risk – Having control over risk exposure International Laser Display Association
Risk management • Goal is to manage and minimize the risk – Tackle football: Wear helmets and padding – Hiking: Carry first aid gear, GPS – Bicycling: Wear helmet, use lights at night International Laser Display Association
Risk management • Goal is NOT to eliminate or water-down the activity to bland nothingness – Only allow touch football – No hiking except on marked paths – All bicycles to have outboard training wheels International Laser Display Association
Risks at discos, nightclubs and concerts • Loud sound systems. One evening too close to the speakers can cause permanent hearing damage – Audiences like loud music (rightly or wrongly) – Note that there is not a movement to turn down sound to OSHA-approved levels • Widespread alcohol consumption – Often to excess • Smoking in many countries • Illegal drugs at some concerts, raves International Laser Display Association
Risks at discos, nightclubs and concerts • Patrons can control risks – Bring earplugs – Stand farther from speakers – Drink in moderation, or non-alcohol drinks • Despite the risks – or maybe BECAUSE of some of the risks – these remain popular • A disco with moderate, OSHA-approved sound levels, that serves only soft drinks, will have very few patrons International Laser Display Association
Risks at discos, nightclubs and concerts • Patrons can control risks – Bring earplugs – Stand farther from speakers – Drink in moderation, or non-alcohol drinks • Despite the risks – or maybe BECAUSE of some of the risks – these remain popular • A disco with moderate, OSHA-approved sound levels, that serves only soft drinks, will have very few patrons International Laser Display Association
Putting it all together. . .
The good and bad of audience scanning Audience scanning -- good Audience scanning - bad • Excellent safety record, despite many shows exceeding MPE • New technique for accurately setting show irradiance • Too many shows exceeding the MPE by far too much • Too many laser show producers setting light levels “by eye” – 4 x the static MPE • Very popular, especially in discos, nightclubs, rock concerts – No idea of the exposure levels • MPE shows are dim, fuzzy – Unacceptable in higher risk environments such as
Patron-managed risk at laser shows • Take conscious or subconscious avoidance actions before the beam crosses the eye – Look away – Blink • Don’t look directly at the projector – Hold up a hand – Stay behind another person’s head – Turn around • Move away from the laser-scanned area International Laser Display Association
A practical proposal to increase audience scanning safety
Requirements for all audience scanning shows • CW lasers only • Operator must measure static beam so as to know irradiance – no more guessing • Well-designed, smooth scan patterns with no hot spots • Effective scan-fail circuit • Laser show operator continuously monitoring the show (or equivalent automated detection system) International Laser Display Association
Level 1 show Below MPE (similar to current regulations) • Laser power at point of closest audience access is below the MPE – Set beam irradiance to 10 m. W/cm 2 – This is the MPE for 1 millisecond pulses • No signage or other warning needed International Laser Display Association
Level 2 Show “With greater power, comes greater responsibility” • Show is allowed to exceed the MPE by a factor of 10 – Measure the static beam; set irradiance to 100 m. W/cm 2 – When scanning, this is 10 x the MPE for 1 millisecond pulses • Signage and caution announcements required – “Caution: Extra-bright laser lights in use. Avoid looking directly into beams” – Similar to signs at amusement parks such as “Do not ride if you are pregnant or have heart problems. ” International Laser Display Association
How does this improve safety? • All audience scanning shows must be measured. NO EXCEPTIONS. • No audience scanning above 10 x the MPE. – This eliminates the very high powered shows at 50, 100, 300 times the MPE • Audience at Level 2 shows have additional safety information – “Avoid looking directly into laser beam” International Laser Display Association
Who will use these levels? • Level 1 shows will be for cautious clients – Corporate shows, family-audience shows, major theme parks • Level 2 shows will be used where patrons accept or even welcome some risks – Discos, nightclubs, rock concerts International Laser Display Association
Use by private sector • Guidelines used by venue owners, show producers in areas where laser laws or enforcement is weak. – They decide whether shows they present are Level 1 or Level 2 • Guidelines championed within the laser show industry (ILDA) International Laser Display Association
Regulatory enforcement • Regulators could informally permit Level 2 shows, if comfortable with professionalism, safety measures of laser show producer – Similar to police enforcement of speed limits: no tickets until you are 10 mph over the 60 mph speed limit International Laser Display Association
Work in standards committees • Seek discussion, improvement and acceptance by standards bodies – IEC 60825 -3, Guidance for laser displays and shows – ANSI Z 136. 10, Safe Use of Lasers in Entertainment, Displays and Exhibitions International Laser Display Association
Conclusion • Audience scanning with visible CW lasers appears to be causing essentially no claimed or proven injuries • There are mechanisms which are reducing the exposure on the retina • For improved safety, we want to eliminate shows which are significantly over the MPE • In return, we ask for shows at a reasonable brightness level International Laser Display Association
Questions?
(Note: Leftover slides are after this point. The leftover slides did not make it into the main presentation given at ILSC 2009. This is usually due to time constraints, but may also be an unfinished thought or line of reasoning. )
Changes vs. injuries
Changes vs. injuries • Changes: Lesion or other visible change to the structure of the eye, which is observable under laboratory conditions • Injury: A change which the person notices, either – Under special conditions such as a uniform blue sky, or – As they go about their daily routine International Laser Display Association
Changes vs. injuries • Changes? Unknown whether audience scanning causes visible lesions on the eye – No studies • Injuries? What is known after 100, 000 people and 11 billion pulses: – Worst case, 25 claimed injuries per decade – Despite most shows being above the MPE, and many being far above the MPE International Laser Display Association
Future studies • Would welcome future studies. For example: – Recruit university students who already go to discos which use lasers. Record their eyes using SDOCT or similar detailed techniques. Let them go to the laser disco as they would normally. After returning • Survey students about their exposure – how many times did the laser enter their eye, was it uncomfortable, etc. • Examine eyes at 1 hour, 24 hours, etc. for changes. International Laser Display Association
To make a show below the MPE • Design show with smooth, always-moving beam effects – No static beams or hot spots • Before show, set beam irradiance to the MPE limit for 1 millisecond pulses (10 m. W/cm 2) • For details, see Makhov’s 2005 paper in Proceedings of the ILSC International Laser Display Association
Makhov’s analysis of laser scan patterns • Pulses (eye crossings) in a show are from 2 milliseconds to 10 microseconds • Within range of thermal MPE • Safest to use MPE for 1 millisecond (10 m. W/cm 2) – This is four times the static MPE Makhov, Greg. Proceedings of the 2005 International Laser Safety Conference, Vol. 7
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