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”
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 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 =
10,950,000,000 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
A typical show
• 3 watt laser
• After optics and scanners, about 1 watt
output toward audience
• 1 milliradian divergence
• Closest audience access 25 meters
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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
International Laser Display Association
Where are the injuries
from 11 billion pulses,
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 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
– (Again, we are not including the July 2009
Tomorrowland incident at this time)
– 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
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
International Laser Display Association
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
International Laser Display Association
Summary
• 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?
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
International Laser Display Association
Important caveats
• Not saying there aren’t changes to retina
– It is unknown whether shows cause laboratorydetectable changes
– Further research would be very helpful
• Not saying the MPEs are wrong
– We believe in and support the MPE levels
International Laser Display Association
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
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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
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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 rerunning 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 10,000,000 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
International Laser Display Association
... 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
0.01 second
5.6 mW/cm2
0.001 second
10 mW/cm2
Typical slow
scanning speed
4x
18 microseconds
27 mW/cm2
Typical fast
scanning speed
10 x
1x
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 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
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
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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
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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
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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
• 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 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 mW/cm2
– 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
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”
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 Z136.10, 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?
(Slides that follow are “leftovers” which may have
been included in various versions previous to this
one)
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Belgian incident
• Tomorrowland dance festival in Boom,
Belgium, July 25-26, 2009
• 90,000 attendees
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Lasers at Tomorrowland
• Multiple lasers used
– Mid-air beams, and audience scanning
– 2 outdoor areas, and 3 indoor tents
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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
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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
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Tomorrowland: Conclusion
• Injuries were not caused by audience
scanning
International Laser Display Association