Eight useful principles of laser light effects for pilots and aviation

1. Eight useful principles of laser light effects for pilots and aviation • Patrick Murphy • International Laser Display Association • LaserPointerSafety.com • January 31, 2012

2. It started with this slide...

3. ... which is completely inaccurate

4. Hazard distances of a5 mW, 1 milliradian green laser pointer

5. Nominal eye hazard to 52 feet

6. Flashblindness hazard to 245 feet

7. Glare hazard to 1,097 feet

8. Distraction hazard to 10,970 feet

9. Keep in mind distances are approximate

10. Superimpose the hazard distances

11. Add 9 more lasers, of different powers and colors

13. Principle #1 The most significant laser hazards have relatively short distances

15. Principle #2 Distraction is always 90% of the total visual interference distance

16. The most significant visual hazards are always10% of the total visual hazard distance • Distraction

17. Principle #3 The eye injury hazard only depends on power and divergence.Visual interference hazards also depend on color.

18. 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.

19. Principle #4 A green laser is more of a visual hazard than an equivalent red or blue laser.

20. A 5 mW, 1 mrad green laser pointer has visual hazard distances that are twice the same laser but in red

22. 29 times difference (88/3)

23. Principle #5 The effect of the laser’s color on visual hazard distances is not linear -- it is the square root

24. 1 W blue laser 3% apparent brightness 4.8 NM visual hazarddistance • 1 W green laser • 88% apparent brightness • 25.5 NM visual hazarddistance • 29x difference in brightness, but… • …only 5.4x difference invisual hazard distance

25. 5 mW red laser 23% apparent brightness 0.9 NM visual hazarddistance • 5 mW green laser • 88% apparent brightness • 1.8 NM visual hazarddistance • 4x difference in brightness, but… • …only 2x difference invisual hazard distance

26. Principle #6 The effect of the laser’s power on all hazard distances is not linear -- it is the square root

27. 500 mW green laser 500 mWpower 18 NM visual hazarddistance • 5 mW green laser • 5 mWpower • 1.8 NM visual hazarddistance • 100x difference in power, but……only 10x difference invisual hazard distance

28. 1 W green laser 1000 mWpower 25.5 NM visual hazarddistance • 1 mW green laser • 1 mWpower • 0.8 NM visual hazarddistance • 1000x difference in power, but……only 31.6x difference invisual hazard distance

30. Principle #6 - restated As lasers get more powerful, the hazard does not increase nearly as fast

31. Principle #6 - restated As lasers get more powerful, the hazard does not increase nearly as fast(good news!)

32. Principle #7 Real-world lasers can have shorter hazard distances than worst-case calculations

33. 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

34. Principle #8 Being inside the NOHD eye hazard distance does not mean automatic damage to eyes

35. 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

36. What most people think the NOHD means • Hazard gradually decreases • Laser light becomes eye-safe just before reaching Nominal Ocular Hazard Distance

37. 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

38. How the NOHD actually works • Substantial safety factor is built in

39. How the NOHD actually works • Substantial safety factor is built in Danger! Caution... OK

40. 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

41. 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

42. That’s why it is theNominal OcularHazard Distance -- not the actual hazard distance

43. 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)

44. 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

45. Implications

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

47. 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

48. 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

49. 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”

50. Summary