Lasers and eye damage

The US attorney general Bill Barr has defended the massive and violent federal response to the demonstration in Portland by arguing that the protestors were the ones who were being violent and that the security forces were just defending themselves and government property.

Barr said federal authorities had a duty to defend against violent attacks and rioters, and said protesters have attempted to burn down the building, shot commercial fireworks, and used pellet guns and slingshots to shoot projectiles that have injured federal officers “to the bone” as well as lasers that have damaged officers’ eyesight.

Are these claims true? Barr is a loyal follower of Donald Trump and hence one must assume that, like Trump, he is lying unless he can prove otherwise. I have not seen a detailed fact-check of those claims of injuries, such as medical reports or independent third party observations.

But my attention was caught by the mention of the eye damage caused by lasers. According to Fox News, Barr even claimed that “three federal agents may suffer permanent blindness after allegedly encountering laser attacks from the crowd.” The initial indications are that it is unsubstantiated and thus can be considered a lie.

“They use lasers to blind the Marshals,” Barr added, echoing a recent White House claim that three federal law enforcement officials were left “blinded” by protesters pointing lasers at their eyes in Portland. An email to the Department of Homeland Security asking the agency to provide evidence or information to back this claim up was not immediately returned.

Barr is clearly seeking to exploit the fear of lasers by those whose only knowledge of them is from films, such as when Goldfinger tries to kill James Bond. (As an aside, Bond villains can never seem to avoid the temptation to use highly elaborate and slow means of killing him. Not only that, after setting in motion the elaborate death scheme, they seem to immediately lose interest and go away, thus giving him time to think of ways to escape.)

Apart from the more powerful (and large) lasers used in research, medical, and weapons facilities, the lasers we encounter in everyday life are the pocket ones used as pointers. It is unlikely that bigger lasers can be taken to demonstrations because that would require also lugging around a powerful power supply. The pocket lasers cannot cause eye damage unless they are aimed straight at the eye for a considerable time.

Eye damage from a pocket laser is unlikely, but could be possible under certain conditions. Red laser pointers that are “properly labeled” in the 3-5 mW range have not caused eye damage — no retinal damage has been reported — but there are very real concerns.

The common red laser pointer is a diode laser, really just a special type of transistor, or diode. Because of the unique features of laser light, it is magnified by 100,000 times as it passes through the eye. The light passes to the back part of the eye, the retina, which is where we perceive vision. The eye actually sees a small part of the electromagnetic spectrum that runs from short cosmic ray energies to long radiowaves. We see only from violet to red. Infrared (IR) and ultraviolet (UV) are just outside our ability to see. The eye is most sensitive to yellow-green light (550 nm). At the same power, 670 nm red light is only 3 percent as bright

In FDA-regulated pointers, the laser power limit is set at one-tenth the actual threshold of damage. If a person sees a bright light, they will automatically blink, on the average in less than 0.2 seconds. This is referred to as the blink reflex, and it is considered when the limit is assigned for how much power will cause an eye injury. By the way, you shouldn’t force a stare at a laser, just like you shouldn’t stare at the sun or any bright light source.

Lasers that are more powerful than the ones used in pointers are commonly used in physics laboratory experiments done by students and I have used them many, many times. The light can reflect off various surfaces and occasionally fleetingly enter the eye but such encounters do not cause damage. While one should never look directly into a laser, during chaotic street demonstrations it would be impossible to aim a laser directly at someone’s eye for anything other than a fleeting moment and so the danger of damage is minimal.

So until Barr provides evidence of such damage, we should assume that he is lying.

And now we hear from Crip Dyke, our very own FtB blogger on the ground in Portland, that after the federal forces left, the protests are once again peaceful.


  1. quantumdad says

    Nowadays, there are companies (Wicked Lasers is the first one that comes to mind, I’m sure there are others) that sell “handheld” lasers (they cannot really be called “pointers” any more) with up to 1 W of power. Such amount of power can cause eye damage even from a diffuse reflection.
    Those lasers are more expensive than a run-of-the-mill laser pointer, but still much cheaper than scientific-grade lasers, and I do not think that their sale is regulated (not as much as scientific/industrial grades lasers, at least).
    So while I still think that the the administration is playing up the fears, I would not just discount this as completely impossible.

  2. jrkrideau says

    I automatically assume any Trump appointee is lying until proven otherwise. If Pompeo said Beijing was the capital of China I would call the Chinese embassy in Ottawa to confirm that the capital had not moved.

  3. says

    The cops deserve no sympathy, not after the dozens they have intentionally and permanently blinded with “rubber bullets” and temporarily with tear gas and pepper spray. Hand held lasers in the eye are a minor inconvenience by comparison.

  4. bmiller says

    I appreciate the use of the word “lying” Mano. We need to ALWAYS respond to such Trump nonsense with a clear understanding of what is going on. Lying.

    My favorite “laser” episode in the media was on C.H.I.P.S. when “Ponch” “saw the laser beam coming towards him” and ducked. (Yes, I am old, and I somehow still remember that!)

  5. sonofrojblake says

    There have been many cases in previous years of people being published for shining lasers at aircraft, especially but not only police helicopters. Surely you’re not saying the panic was overstated?

  6. lorn says

    I don’t remember the rated power but an acquaintance I see occasionally hanging around a local reptile shop was playing with a green laser sold as a distress beacon/ flare. At about six inches it could set a piece of white paper with black printing alight in a few seconds. It was clearly much quicker on the dark spots and was possible, by scanning quickly, to burn out the lettering and leave the blank paper relatively intact. He complained that it used up batteries pretty quickly.

    As I remember it the unit was about 10″ long and roughly 1-1/2″ in diameter. I suspect that this unit might cause some damage, even if temporary.

    Of course a whole lot of people know about potential damage from lasers. Shining lasers at aircraft is pretty much established as a thing on YouTube with lots of examples. The local police helicopter pilots are reported as wearing protective googles that greatly reduce the risk. Reports that I hear are that US troops have similar protective gear.

  7. says

    Whether or not hand-held lasers can cause much damage to an eye the burden of proof for any claim is always on the claimant. Barr’s claim is specific (three people with possible permanent injuries). If they know how many people were injured they know how to document their injuries and provide evidence for the truth of the claim. If Barr cannot offer evidence to support his claim we are justified in rejecting it.

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