scanning audiences at laser shows: theory and practice

Scanning Audiences at Laser Shows:

Theory and Practice ... and a Proposal

Patrick Murphy, ILDA Executive DirectorGreg Makhov, ILDA Safety Committee Chair

What is Audience What is Audience Scanning?Scanning?

“Creating beautiful mid-air beam patterns

which surround and envelop the audience,

for entertainment and display purposes”

http://upload.wikimedia.org/wikipedia/en/8/8b/Lasers_audience-scanning-in-rimini.jpg

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

How many peopleHow many peoplehave been exposed?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


109,500,000 people x 100 pulses per show =

10,950,000,000 pulsesover 30 years

What laser power have theseWhat laser power have these110 million people110 million peoplebeen exposed to?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


What is the irradianceat the audience?

• Exact irradiance unknown• Estimates from laser show and safety

experts– Greg Makhov, John O’Hagan, James Stewart

• Most shows are above the MPEat the point of closest audience access

• Many shows are far above the MPE– 10, 50, 100 ... even 300 times the MPE


A typical show• 3 watt laser• After optics and scanners, about 1

watt output toward audience• 1 milliradian divergence• Closest audience access 25 meters


A typical show, cont.• Static irradiance: 162 mW/cm2 – 65x the ¼ second MPE

• Well-designed scanning effects, no static beams– Dwell time is 1 msec or less, so single

pulse MPE applies• Because of scanning, hazard is

reduced 4x– 16x the single pulse MPE


Where are the injuriesWhere are the injuriesfrom 11 billion pulses,from 11 billion pulses,most over the MPE?most over the MPE?

“Close to zero” injuries

“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 SystemsProceedings 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 ShowShneck, Marina MD; Levy, Jaime MD; Klemperer, Itamar MD; Lifshitz, Tova MDDepartment of Ophthalmology, Soroka University Medical Center, Ben-Gurion University of the NegevRetinal 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– (Again, we are not including the July 2009

Tomorrowland incident at this time)– Not even informal complaints on blogs

or forums


“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


Recent incidents• July 2008, Aquamarine Festival, near Moscow– 35+ persons injured by pulsed laser– Due to rain forcing audience into a tent, the laser

was irresponsibly and illegally aimed down into audience instead of up into the sky

–Wrong type of laser; pulsed lasers should never be used for audience scanning

– Because of illegal use, these injuries do not apply to statistics about continuous-wave lasers used for audience scanning


Recent incidents• July 2009, Tomorrowland Festival, Belgium– 2 persons (out of 90,000) had eye injuries– Laser show irradiance was calculated to be

close to or at MPE: 50 mW/cm² closest to audience (5x MPE), 10 mW/cm² at 20 meters into crowd (same as MPE)

–Many high-powered laser pointers in use in crowd

– Conclusion: Legal and safety authorities agreed injuries were due to crowd laser pointers


Summary• Based on Based on 1996 study finding 5 1996 study finding 5

incidents over 20 yearsincidents over 20 years• 2.5 reported injuries 2.5 reported injuries per decadeper decade

• Estimating 90% underreporting:Estimating 90% underreporting:• 25 estimated injuries 25 estimated injuries per decade, per decade,

worldwideworldwide

How does this compare?Lasers U.S. amusement park rides• 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

Important caveats• Not saying there aren’t changes to

retina– It is unknown whether shows cause

laboratory-detectable changes– Further research would be very helpful

• Not saying the MPEs are wrong–We believe in and support the MPE

levels


Our conclusion• We are saying that, after 30 years and 11

billion pulses, most over the MPE, there are practically no complaints, injury claims, proven injuries, lawsuits, etc. from audience members, from CW shows.

• If there were, these shows would not be occurring– Clients were very skittish after press reports

of July 2008 injuries caused by pulsed laser


Why are there essentiallyWhy are there essentiallyno reported injuries?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



• 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



• Multiple pulses are safer than previously thought– Effect of multiple pulses not n-1/4

– See papers presented earlier at ILSC 2009



• 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%



• 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



• Avoidance response beforebeam 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

themInternational Laser Display

Association


• 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


Is it possible to create Is it possible to create shows which are below the shows which are below the

MPE?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


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 10,000,000 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 t3/4 x 10-3 J/cm2


... compare to MPEs ...Exposure time MPE Notes Time

compared to aversion response

1.0 second 1.8 mW/cm2 Aversion response

protects against this exposure

0.25 second 2.5 mW/cm2 Longest exposure

needed to be considered

1x

0.01 second 5.6 mW/cm2 2.2 x0.001 second 10 mW/cm2 Typical slow

scanning speed4 x

18 microseconds

27 mW/cm2 Typical fast scanning speed

10 xInternational 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.


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 mW/cm2 (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


Problem:Problem:MPE-level shows are not MPE-level shows are not

impressiveimpressive

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


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


Solution lies inSolution lies inrisk analysisrisk analysis

and managementand 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


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)


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


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


Risk management• Goal is NOT to eliminate or water-

downthe activity to bland nothingness– Only allow touch football– No hiking except on marked paths– All bicycles to have outboard training

wheels


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


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


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


Putting it all together...Putting it all together...

The good and badof audience scanning

Audience scanning -- good• Excellent safety record,

despite many shows exceeding MPE

• New technique for accurately setting show irradiance– 4x the static MPE

• Very popular, especially in discos, nightclubs, rock concerts

Audience scanning - bad• Too many shows

exceeding the MPE by far too much

• Too many laser show producers setting light levels “by eye”– No idea of the exposure

levels• MPE shows are dim, fuzzy

– Unacceptable in higher risk environments such as discos, nightclubs, concerts

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 areaInternational Laser Display

Association

A practical proposal to A practical proposal to increase audience scanning increase audience scanning

safetysafety

Requirements forall 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)


Level 1 showBelow MPE (similar to current regulations)• Laser power at point of closest

audience access is below the MPE– Set beam irradiance to 10 mW/cm2

– This is the MPE for 1 millisecond pulses• No signage or other warning needed


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

mW/cm2

– When scanning, this is 10x 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 10x 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”


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


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)


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


Work in standards committees

• Seek discussion, improvement and acceptance by standards bodies– IEC 60825-3, Guidance for laser displays

and shows– ANSI Z136.10, Safe Use of Lasers in

Entertainment, Displays and Exhibitions


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


Questions?Questions?

(Slides that follow are “leftovers” which may have been included in various versions

previous to this one)


Belgian incident• Tomorrowland dance festival in

Boom, Belgium, July 25-26, 2009• 90,000 attendees


Lasers at Tomorrowland• Multiple lasers usedMultiple lasers used– Mid-air beams, and audience Mid-air beams, and audience

scanningscanning– 2 outdoor areas, and 3 indoor tents2 outdoor areas, and 3 indoor tents


Eye injury report• 2 people claimed eye injuries– “Irreversible” central visibility to a young man– Unspecified eye damage to a 21-year-old woman

• Complaint lodged with police against festival organizer

• Found to be caused by laser pointer in crowd– Police, mayor, health officials, organizer agree–Many witnesses to high-powered pointer use


Laser show did not cause the injury

• Only 2 persons out of 90,000 claimed injury– Compare with Moscow festival: 35+ claims– Compare with Bulgarian disco: 12+ injury claims

• Company used “beam attenuation maps”• Audience irradiance: 50 mW/cm² closest to

audience, 10 mW/cm² 20 meters in crowd• Show was continuously monitored• Police, mayor allowing same festival in 2010


Tomorrowland: Conclusion• Injuries were not caused by audience

scanning


scanning audiences at laser shows: theory and practice

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