Eight useful principles of laser light effects for pilots and

aviation

Patrick Murphy

International Laser Display AssociationLaserPointerSafety.com

January 31, 2012

It started with this slide...

... which is completely inaccurate

Hazard distances of a5 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

The most significant laser hazards have

relatively short distances

Principle #1

Distraction is always 90% of the total visual interference distance

Principle #2

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

•Distraction

The eye injury hazard only depends on power and

divergence.

Visual interference hazards also depend on color.

Principle #3

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.

A green laser is more of a visual hazard than

an equivalent red or blue laser.

Principle #4

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)29 times difference (88/3)

The effect of the laser’s color on visual hazard distances is not linear -- it is the

square root

Principle #5

• 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

• 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

The effect of the laser’s power on all hazard distances is not linear -- it is the

square root

Principle #6

• 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, but…

…only 10x difference invisual hazard distance

• 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, but…

…only 31.6x difference invisual hazard distance

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 #6 - restated

Real-world lasers can have shorter hazard

distances than worst-case calculations

Principle #7

• 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

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

Principle #8

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

• Hazard gradually decreases

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

Danger! Caution... OK

How the NOHD actually works

• Substantial safety factor is built in

How the NOHD actually works

• Substantial safety factor is built in

Danger!Caution... OK

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 theNominal 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?