by Jason Harlow
, original version May 2013, latest revision Nov. 2018
On May 28, 2012 the Toronto Star headline was Laser Attacks on Pilots are on the Rise, Records Show, and the article contained the phrase "While the immediate concern is keeping control of the aircraft, for pilots there is also the worry of suffering a long-term eye injury that can keep them grounded." Occasionally I have used 5 milliWatt class 3A green laser-pointers at "star parties". A star party is an outdoor gathering at night, often with a telescope, to look at the stars. Green light scatters off air and dust much better than red light, so when you shine a green laser up into the night sky you can easily see the beam itself. That way, it can be used as a convenient pointer to point out constellations and planets to a large group of people.
So I have been wondering if, (a) my lasers could accidentally
cause long-term eye injuries to pilots far above, and (b) my
lasers might accidentally be distracting to the pilots far
I took 3 different green laser pointers, all 5 mW, all of which were purchased for less than $50 each. I measured the spot size at 1, 10, 15, 40 and 97 m. I then plotted distance versus beam diameter and did a best-fit linear slope. I found a slope of 1.04 +/- 0.09 mm/m and a y-intercept of 1.4 +/- 0.5 mm. This means that, at the laser pointer itself, the beam diameter is about 1.5 mm. As it travels, the diameter increases by 1 mm for every 1 m away from the laser pointer.
At a distance of 5 m away from the laser, the beam diameter is
7 mm, which is a typical diameter of the dark-adapted pupil
(Bradley JC, Bentley KC, Mughal AI, Bodhireddy H and Brown SM
2011, Journal of Refractive Surgery, v.27 issue.3,
pg.202). This means that if you are within 5 m of
the laser and it is shot directly into one of your dark-adapted
pupils, all 5 mW of power will enter your eye, and then be
focused onto your retina.
At a distance of 10 m, the beam diameter is 12 mm, and its area is 110 sq-mm. Since a 7 mm-diameter dark-adapted pupil has an area of 34 sq-mm, only 1.5 mW of power will enter your eye if this laser is shot directly in.
At 100 m, the beam is 10 cm in diameter with an area of 8700 sq-mm, which is 250 times bigger than your dark-adapted pupil. The maximum power which can enter your eye at this distance is 0.02 mW.
At a distance of 1 km, which would be typical for a low-flying aircraft, the maximum power which could enter a pilot's eye is 0.0002 mW, or 0.2 micro-Watts.
Note that Class 1 lasers have powers less than 0.024 mW, and they carry no warning label because they are incapable of causing eye damage. My little experiment indicates that a Class 3A laser-pointer (5 mW) becomes equivalent to a Class 1 laser at a distance of 90 m or farther.
As for actual retinal damage, it has been estimated that it would take 10 seconds of staring directly into a class 3A laser in order to damage your retina. But, in practice this is impossible to do because it feels very painful and you immediately look away. [See http://www.drgreene.com/qa/laser-pointers for a nice discussion of this.]
In answer to my questions above, I think that (a) a pilot could
not suffer a long-term eye injury from getting accidentally shot
with my class 3A laser on the ground. There have been no reports
of a long-term eye injury being caused by a class 3A laser even
at point-blank range, and for a pilot more than 100 m away from
the laser, it seems impossible.
In answer to (b), I found, somewhat surprisingly, that
laser-light shining into your eye is quite distracting and
annoying, even in daytime conditions! If it was night,
this could temporarily eliminate your night vision, and leave
big spots in your vision that could be dangerous if you are
trying to operate a vehicle, like a plane for
example. In, 2018 I was contacted by a professional
pilot, Ryan Zorgdrager, who stated that:
"When a laser strike happens the light is often refracted and spread throughout the cockpit due to scratches in the window and the angle the light relative to the window, lighting up the whole cockpit. Side effects are loss of night vision and flash blindness in the short term."
This makes sense, and I can understand that blinding the pilots
of an aircraft is a big danger to everyone, not just the
pilots. So, I think the basic answer is that, yes, the
short-term effects of laser-induced blindness or distraction
could quite be dangerous to pilots, and people should definitely
be aware of this. I may have to rethink my star party
I also have been notified, again by this professional pilot,
that although my laser usage has certainly never been malicious,
simply using these green lasers at star parties could be
illegal, and I think it's wise to take note of federal
. Good information!