Eight useful principles of laser
light effects for pilots and
aviation
Patrick Murphy
International Laser Display Association
LaserPointerSafety.com
January 31, 2012
It started with this slide...
... which is completely inaccurate
Hazard distances of a
5 mW, 1 milliradian green laser pointer
Nominal eye hazard to 52 feet
Flashblindness hazard to 245 feet
Glare hazard to 1,097 feet
Distraction hazard to 10,970 feet
Keep in mind distances are approximate
Superimpose the hazard distances
Add 9 more lasers, of different
powers and colors
Principle #1
The most significant
laser hazards have
relatively short
distances
Principle #2
Distraction is always
90% of the total visual
interference distance
The most significant visual hazards are always
10% of the total visual hazard distance
• Distraction
Principle #3
The eye injury hazard only
depends on power and
divergence.
Visual interference hazards
also depend on color.
Both 1 watt, 1 milliradian lasers have an
eye hazard distance of 733 feet.
But because one is green and one is blue, the visual
interference distances are very different.
Principle #4
A green laser is more
of a visual hazard than
an equivalent red or
blue laser.
A 5 mW, 1 mrad green laser pointer has
visual hazard distances that are twice the
same laser but in red
29 times difference (88/3)
Principle #5
The effect of the
laser’s color on visual
hazard distances is
not linear -- it is the
square root
• 1 W green laser
• 1 W blue laser
• 88%
apparent
brightness
• 3%
apparent
brightness
29x
difference in
brightness, but…
• 25.5 NM
visual hazard
distance
• 4.8 NM
visual hazard
distance
…only 5.4x
difference in
visual hazard
distance
29 = 5.4
• 5 mW green laser
• 5 mW red laser
• 88%
apparent
brightness
• 23%
apparent
brightness
4x
• 1.8 NM
visual hazard
distance
• 0.9 NM
visual hazard
distance
…only 2x
difference in
visual hazard
distance
difference in
brightness, but…
4=2
Principle #6
The effect of the
laser’s power on all
hazard distances is
not linear -- it is the
square root
• 5 mW green laser
• 500 mW green laser
• 5 mW
power
• 500 mW
power
• 1.8 NM
visual hazard
distance
• 18 NM
visual hazard
distance
100x
difference in power,
but…
…only 10x
difference in
visual hazard
distance
100 = 10
• 1 mW green laser
• 1 W green laser
• 1 mW
power
• 1000 mW
power
• 0.8 NM
visual hazard
distance
• 25.5 NM
visual hazard
distance
1000x
difference in power,
but…
…only 31.6x
difference in
visual hazard
distance
1000 = 31.6
Principle #6 - restated
As lasers get more
powerful, the hazard
does not increase
nearly as fast
Principle #6 - restated
As lasers get more
powerful, the hazard
does not increase
nearly as fast
(good news!)
Principle #7
Real-world lasers can
have shorter hazard
distances than worstcase calculations
•
A laser’s 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 beam’s
power over a larger area
• 1 mrad on chart but 1.5 mrad actual
Principle #8
Being inside the
NOHD eye hazard
distance does not
mean automatic
damage to eyes
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
What most people think the NOHD means
•
•
Hazard gradually decreases
Laser light becomes eye-safe just before
reaching Nominal Ocular Hazard Distance
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
How the NOHD actually works
•
Substantial safety factor is built in
How the NOHD actually works
Danger!Caution... OK
•
Substantial safety factor is built in
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
How the NOHD was developed (2 of 2)
•
Nominal Ocular Hazard Distance is the distance at
which the laser beam’s 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
That’s why it is the
Nominal Ocular
Hazard Distance -not the actual hazard
distance
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
√10 (3.16)
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
Implications
Implications
•
Helps to explain why, after 10,000+ FAA
laser/aircraft incidents, there have been no
permanent eye injuries (medically determined
retinal lesions)
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
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
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”
Summary
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
8 useful principles of laser light effects
3. Eye injury distance (NOHD) depends on
power and divergence. Visual interference
hazard distances also depend on color.
4. A green laser is more of a visual hazard
than an equivalent red or blue laser
5. Color (visual efficacy) has a square root effect
on hazard distances
8 useful principles of laser light effects
6. Power has a square root effect on hazard
distances
a. As lasers get more powerful, the hazard
distance does not increase nearly as fast
7. Real-world lasers can have shorter hazard
distances than worst-case calculations
8 useful principles of laser light effects
8. Being inside the NOHD eye hazard distance
does not mean automatic damage to eyes
a. There is a large safety factor built in to the
Nominal Ocular Hazard Distance
b. At the NOHD/3.16 distance, there is a 50/50
chance of causing a minimally detectable
retinal lesion under optimum conditions
Questions?