Title: Eight useful principles of laser light effects for pilots and aviation
1Eight useful principles of laser light effects
for pilots and aviation
- Patrick Murphy
- International Laser Display Association
- LaserPointerSafety.com
- January 31, 2012
2It started with this slide...
3... which is completely inaccurate
4Hazard distances of a5 mW, 1 milliradian green
laser pointer
5Nominal eye hazard to 52 feet
6Flashblindness hazard to 245 feet
7Glare hazard to 1,097 feet
8Distraction hazard to 10,970 feet
9Keep in mind distances are approximate
10Superimpose the hazard distances
11Add 9 more lasers, of different powers and colors
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13The most significant laser hazards have
relatively short distances
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15Distraction is always 90 of the total visual
interference distance
16The most significant visual hazards are always
10 of the total visual hazard distance
17The eye injury hazard only depends on power and
divergence.Visual interference hazards also
depend on color.
18Both 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.
19A green laser is more of a visual hazard than an
equivalent red or blue laser.
20A 5 mW, 1 mrad green laser pointer has visual
hazard distances that are twice the same laser
but in red
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2229 times difference (88/3)
23The effect of the lasers color on visual hazard
distances is not linear -- it is the square root
24- 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
25- 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
26The effect of the lasers power on all hazard
distances is not linear -- it is the square root
27- 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
28- 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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30As lasers get more powerful, the hazard does not
increase nearly as fast
31As lasers get more powerful, the hazard does not
increase nearly as fast(good news!)
32Real-world lasers can have shorter hazard
distances than worst-case calculations
33- 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
34Being inside the NOHD eye hazard distance does
not mean automatic damage to eyes
35NOHD 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
36What most people think the NOHD means
- Hazard gradually decreases
- Laser light becomes eye-safe just before reaching
Nominal Ocular Hazard Distance
37What most people think the NOHD means
Danger!
Caution...
OK
- Hazard gradually decreases
- Laser light becomes eye-safe just before reaching
Nominal Ocular Hazard Distance
38How the NOHD actually works
- Substantial safety factor is built in
39How the NOHD actually works
Danger!
Caution...
OK
- Substantial safety factor is built in
40How 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
41How 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
42Thats why it is theNominal OcularHazard
Distance -- not the actual hazard distance
43NOHD 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)
44NOHD 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
45Implications
46Implications
- Helps to explain why, after 10,000 FAA
laser/aircraft incidents, there have been no
permanent eye injuries (medically determined
retinal lesions)
47Implications
- 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
48Implications
- 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
49Example
- 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
50Summary
518 useful principles of laser light effects
- The most significant hazards are relatively close
to the laser - Distraction is always 90 of the total visual
hazard distance
528 useful principles of laser light effects
- Eye injury distance (NOHD) depends on power and
divergence. Visual interference hazard distances
also depend on color. - A green laser is more of a visual hazard than an
equivalent red or blue laser - Color (visual efficacy) has a square root effect
on hazard distances
538 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
548 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
55Questions?
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