Eight useful principles of laser light effects for pilots and aviation

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Eight useful principles of laser light effects
for pilots and aviation

• Patrick Murphy
• International Laser Display Association
• LaserPointerSafety.com
• January 31, 2012

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It started with this slide...
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... which is completely inaccurate
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Hazard distances of a5 mW, 1 milliradian green
laser pointer
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Nominal eye hazard to 52 feet
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Flashblindness hazard to 245 feet
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Glare hazard to 1,097 feet
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Distraction hazard to 10,970 feet
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Keep in mind distances are approximate
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Superimpose the hazard distances
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Add 9 more lasers, of different powers and colors
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The most significant laser hazards have
relatively short distances

• Principle 1

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Distraction is always 90 of the total visual
interference distance

• Principle 2

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The most significant visual hazards are always
10 of the total visual hazard distance

• Distraction

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The eye injury hazard only depends on power and
divergence.Visual interference hazards also
depend on color.

• Principle 3

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Both 1 watt, 1 milliradian lasers have aneye
hazard distance of 733 feet.But because one is
green and one is blue, the visual interference
distances are very different.
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A green laser is more of a visual hazard than an
equivalent red or blue laser.

• Principle 4

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A 5 mW, 1 mrad green laser pointer has visual
hazard distances that are twice the same laser
but in red
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29 times difference (88/3)
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The effect of the lasers color on visual hazard
distances is not linear -- it is the square root

• Principle 5

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• 1 W green laser
• 88 apparent brightness
• 25.5 NM visual hazarddistance

• 1 W blue laser
• 3 apparent brightness
• 4.8 NM visual hazarddistance

• 29x difference in brightness, but
• only 5.4x difference invisual hazard distance

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• 5 mW green laser
• 88 apparent brightness
• 1.8 NM visual hazarddistance

• 5 mW red laser
• 23 apparent brightness
• 0.9 NM visual hazarddistance

• 4x difference in brightness, but
• only 2x difference invisual hazard distance

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The effect of the lasers power on all hazard
distances is not linear -- it is the square root

• Principle 6

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• 5 mW green laser
• 5 mWpower
• 1.8 NM visual hazarddistance

• 500 mW green laser
• 500 mWpower
• 18 NM visual hazarddistance

• 100x difference in power, butonly 10x
  difference invisual hazard distance

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• 1 mW green laser
• 1 mWpower
• 0.8 NM visual hazarddistance

• 1 W green laser
• 1000 mWpower
• 25.5 NM visual hazarddistance

• 1000x difference in power, butonly 31.6x
  difference invisual hazard distance

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As lasers get more powerful, the hazard does not
increase nearly as fast

• Principle 6 - restated

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As lasers get more powerful, the hazard does not
increase nearly as fast(good news!)

• Principle 6 - restated

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Real-world lasers can have shorter hazard
distances than worst-case calculations

• Principle 7

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• A lasers advertised power may be more than its
  actual power
• 1 W advertised but only 800 mW actual
• At higher powers, real-world lasers may have
  higher divergence, thus spreading the beams
  power over a larger area
• 1 mrad on chart but 1.5 mrad actual

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Being inside the NOHD eye hazard distance does
not mean automatic damage to eyes

• Principle 8

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NOHD of a 1 watt, 1 milliradian laser

• 733 feet Nominal Ocular Hazard Distance
• Note this is worst-case -- normally 1.5 to 2
  mrad, giving a shorter NOHD of 489 to 367 feet

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What most people think the NOHD means

• Hazard gradually decreases
• Laser light becomes eye-safe just before reaching
  Nominal Ocular Hazard Distance

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What most people think the NOHD means
Danger!
Caution...
OK

• Hazard gradually decreases
• Laser light becomes eye-safe just before reaching
  Nominal Ocular Hazard Distance

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How the NOHD actually works

• Substantial safety factor is built in

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How the NOHD actually works
Danger!
Caution...
OK

• Substantial safety factor is built in

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How the NOHD was developed (1 of 2)

• Lasers aimed into animals eyes
• Power gradually increased
• Power level where lesions began to be seen in 50
  of animals is called ED50
• For visible, continuous light at 1/4 second
  exposure, ED50 25.4 mW/cm2
• Safe human exposure set to be 10 times less than
  ED50
• 2.54 mW/cm2 becomes Maximum Permissible Exposure
  (MPE) for visible CW light, 1/4 sec. exposure

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How the NOHD was developed (2 of 2)

• Nominal Ocular Hazard Distance is the distance at
  which the laser beams irradiance falls below the
  MPE
• At aircraft distances and for consumer lasers,
  depends on power and on beam divergence
• Example 1 watt laser with 1 milliradian
  divergence, NOHD is 733 feet

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Thats why it is theNominal OcularHazard
Distance -- not the actual hazard distance
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NOHD of a 1 watt laser,with ED50 distance shown

• 1 Watt laser, 1 milliradian divergence
• 733 feet Nominal Ocular Hazard Distance
• 232 feet ED50 distance
• ED50 distance is always NOHD divided by v10 (3.16)

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NOHD of a 1 watt laser,with ED50 distance shown

• At ED50 distance, under laboratory conditions,
  there is a 50/50 chance that a laser can create a
  minimally detectable lesion
• Beyond ED50 distance, chance of a minimally
  detectable lesion falls off

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Implications
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Implications

• Helps to explain why, after 10,000 FAA
  laser/aircraft incidents, there have been no
  permanent eye injuries (medically determined
  retinal lesions)

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Implications

• Helps to explain how over 109 million people have
  been exposed to 11 billion flashes of laser light
  -- often well over the MPE -- at audience
  scanning laser shows, with only about 8 probable
  cases of retinal injuries after 30 years of
  shows

Shows using visible, continuous-wave laser light
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Implications

• Gives confidence to police pilots needing to
  search for active laser misuse, that the
  likelihood of eye injury is significantly less
  than the NOHD might indicate

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Example

• A 1 watt laser, about the most powerful commonly
  available consumer laser
• 733 feet NOHD at a very conservative 1
  milliradian divergence
• 489 feet NOHD at a more realistic 1.5 mrad
• 155 feet ED50 distance at 1.5 mrad
• At 155 feet from the laser, there is a 50/50
  chance of getting a minimally detectable retinal
  lesion under optimum (laboratory) conditions

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Summary
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8 useful principles of laser light effects

1. The most significant hazards are relatively close
   to the laser
2. Distraction is always 90 of the total visual
   hazard distance

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8 useful principles of laser light effects

1. Eye injury distance (NOHD) depends on power and
   divergence. Visual interference hazard distances
   also depend on color.
2. A green laser is more of a visual hazard than an
   equivalent red or blue laser
3. Color (visual efficacy) has a square root effect
   on hazard distances

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8 useful principles of laser light effects

• Power has a square root effect on hazard
  distances
• As lasers get more powerful, the hazard distance
  does not increase nearly as fast
• Real-world lasers can have shorter hazard
  distances than worst-case calculations

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8 useful principles of laser light effects

• Being inside the NOHD eye hazard distance does
  not mean automatic damage to eyes
• There is a large safety factor built in to the
  Nominal Ocular Hazard Distance
• At the NOHD/3.16 distance, there is a 50/50
  chance of causing a minimally detectable retinal
  lesion under optimum conditions

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Questions?
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