A comprehensive resource for safe and responsible laser use
Laser use during protests
Why lasers are used at protests
- Aiming at authorities to distract or temporarily flashblind them. This might be done to disrupt the authorities' view of the people in front of them (e.g., those holding the lasers). Or it could be more planned, as a diversion to draw authorities' attention from another area of the protest.
- Aiming at camera sensors to temporarily flashblind, or permanently disable cameras. This was done in the August 2019 Hong Kong protests to try and shut down facial recognition systems used against protesters.
- Aiming at buildings, helicopters, crowds, etc. to gain attention. This is the visual equivalent of shouting or chanting. There is no intent to harm or do anything other than to express displeasure against a target such as a police station, or to gain attention for the protest. (Of course, aiming lasers at people and aircraft is potentially hazardous and thus may have unintended consequences.)
- Aiming at authorities to try to inflict eye or skin injuries. Powerful handheld lasers may cause eye injuries at close range. However, serious or permanent injuries do not generally occur for reasons discussed elsewhere on this page. (Be wary of any official accounts of eye injuries. They may not be accurate unless the patient has been assessed by an expert with experience in laser eye injuries.) As for skin injuries, usually handheld lasers are not powerful enough to injure uncooperative persons' bare skin at any reasonable distance. Also, the person will feel the heat build up and should be able to move or turn away before any significant burn occurs.
Defending against laser attacks
- Persons directly illuminated by laser beams can blink, look down or look away. This reduces the amount of time the laser is in the eye and thus reduces any heat buildup. (Injuries from visible laser light are possible when the eye's lens focuses the light onto the retina. Whether an actual injury occurs depends on the power of the laser and the length of time it is in any one place on the retina. Also, by looking away, if there is an injury it would not be in the center of the visual field which is most important for good vision.)
- Helmet shields can be equipped with tinted laser-absorbing strips that reduce the light brightness. Usually these are effective against the most common laser color used at protests, green, but advanced strips may also protect against other colors. Photos and a description of such a laser-absorbing strip is at a news story here. An advantage of the strip is that the wearer just tilts his or her head down so they are looking out the strip; nothing needs to be put on as is the case with glasses.
- Laser glare protection eyewear may be used by pilots or others facing constant laser harassment, who need to protect a full visual field (not just a strip). Some police air services and demonstration officers have been issued such anti-laser glasses.
- Laser-wielding demonstrators generally can be easily identified. The visible laser beam points right back to the person holding it. Police can counter in real-time (arrest) or can use photos/video to later try to apprehend laser attackers.
- Police can use bright light as well. In the August 2019 protests, the Hong Kong Journalists' Association accused police of aiming "strong flashlights" at journalists to obstruct their reporting.
Lasers at protests are unlikely to cause eye injuries
In terms of causing eye injuries to police, in general lasers are not effective. Even if a person wanted to cause an injury, it is hard to do so by handholding a low-power laser beam on an uncooperative person many yards or meters away who can close his or her eyes, or who can simply look away.
Authorities or the press may try to indicate these are dangerous weapons. During the August 2019 Hong Kong protests, police held a press conference where they showed a laser at a close range (roughly 20 inches or 1/2 meter) being steadily aimed at a motionless sheet of newspaper:
After a few seconds of being held on a dark (light-absorbing) part of the newspaper, smoke appeared:
However, in real-world protest conditions it is much less likely the laser could burn the paper. At longer distances such as from a protester to a police officer it is harder to keep the laser on a single spot so that heat builds up. The target can blink or move. The beam spreads as it travels, lessening the light energy density (a larger beam "dot").
To counteract the police claims, a protester held up a newspaper while dozens of lasers tried to burn it — "without success" according to a news story.
This is not to say that laser light is completely safe, or that it should be deliberately aimed at anyone's head. Ordinary citizens, police and other non-laser experts should never deliberately aim a laser at a person's head or eyes. The risk of injury depends on many factors, such as the laser power, divergence (beam spread), distance, steadiness, etc. Because non-experts cannot fully evaluate the risk, it is safest and most humane to keep lasers away from heads and eyes.
Hong Kong police did claim potential injuries. They said "three of our officers received medical treatment after protesters shined laser guns at them." The nature of any injury was not reported.
Anyone hit by a beam, and concerned about injuries or aftereffects, should read the page "If you are hit by a laser beam."
Lasers can block or damage cameras
For blocking the view to be effective, the laser's light would need to stay on the camera lens. In most cases, as soon as the laser is taken away, the view returns.
If the laser is powerful enough, the sensor can be damaged. This may take the form of dark spots where the laser was brightest, or of horizontal or vertical lines where the laser damaged an entire row of pixels. Since the "injury" is localized, the rest of the camera sensor may continue to work.
Demonstrators would not know whether a given camera was damaged, unless they could somehow see its output.
Persons in the area where laser pointers are being used should take care with a camera. This includes smartphone lenses, and still and video cameras. A single direct hit from a powerful laser may permanently damage the sensor. This damage can occur even if the camera is turned off if there is no physical shutter on the lens, as with smartphones and some mirrorless cameras. Journalists may wish to use lower-cost cameras to take photos or videos when laser beams are coming towards them. This avoids damaging expensive top-of-the-line equipment.
It should be noted that camera sensors are more sensitive to bright light damage than the human retina. So the fact that a camera sensor was damaged does not automatically mean that an eye would also be injured by the same laser under the same conditions.
Are lasers "offensive weapons"?
To give an analogy, kitchen knives are widely available and are not considered to be weapons when used at home for cooking or cutting objects. But if a person carries a kitchen knife to a rally — or worse, pulls it out and aims it towards an officer — then it could be considered as an "offensive weapon."
In addition, the nature of the "weapon" should be considered. If a person has a butter knife on them (e.g. a legal 1 or 5 mW laser pointer), this is different than having a steak knife or carving knife (higher powered handheld laser).
Finally, the nature of the target should also be considered. If cameras are important to police, and they can be blocked or damaged by laser light, then this could also be considered as "weapon" use. The intent is to deny police one of their crowd control tools. (As to whether surveillance camera information is misused, that is a political question that might differ in each case or jurisdiction.)
Here is a potential "weapon" use: In November 2019 in Chile, demonstrators aimed dozens of laser pointers at a drone, thought to be a police surveillance drone. Video shows the drone waver and eventually fly or drop to the ground. It is not known if the drone's camera sensor was temporarily or permanently blinded causing the drone pilot to lose control, or whether the pilot decided to land the aircraft. Either way, the demonstrators were successful in stopping any surveillance. (Details and links here.)
On the other hand, if lasers are used simply to make a dramatic point, such as aiming them at a building, this is not a "weapon" but instead goes back to the purpose of a laser pointer: to point out or draw attention to objects of interest. This assumes the lasers are not deliberately aimed at occupied windows or cameras on a building, but are just used to make patterns on a building as shown below.
Lasers compared to knives as weapons
- Both are useful tools which can become weapons when used with ill intent.
- Both come in many different types, which can have very different damage potential.
For example, low-powered pointers are safe for household use by adults, while higher powered handheld lasers should only be wielded by someone knowledgeable and cautious about their danger.
Knifes cause much more harm than lasers
However, there are also significant differences between lasers and knives as weapons.
As the text at the bottom of the graphic indicates, knives are much, much more hazardous than lasers.
For one thing, laser safety distances such as the NOHD are usually very conservative. Laser beams do spread out with distance; this reduces the energy in any one area. For this reason, noticeable or significant injury does not occur until much closer to the laser device than the conservative, "safe" distance.
For another thing, it is usually easier to defend against a laser attack. A person can close their eyes or look away to reduce or eliminate any harmful eye injuries.
About the pictures
The lasers pictured in the graphic give a general idea of the output. But note that a single type of laser such as the "Laser 303" shown for the 500 mW illustration, can come in powers from 10 to 1000 mW. For this reason, don't use the illustrations to determine the power of a laser you might have.
Also, the information printed on a laser about its power output may be wildly inaccurate.
- It could be too low, in the case of lasers marked as being <1 mW or <5 mW but which may actually be in the tens or even 100s of milliwatts. This can be detrimental to public safety.
- Or the marked output may be too high, in the case of lasers sold as 2 to 5 watts (2000 to 5000 mW) but which may actually be as low as 50 mW.
Police and the press should be especially aware that the information printed on a laser device may be inaccurate.
Details and additional information
Eye injuries from exposure to lasers at protests
- As of 2019, there have been relatively few protests with reported eye injuries. See the links above ("News reports of lasers being used in demonstrations") to look for stories of protests, to see if there are any with claimed eye injuries.
Any such claims by the authorities or in the press should be treated with caution.
- A laser beam close up is more hazardous than one at a distance, as shown by the diagram. Lasers that can burn newspapers or ignite cigarettes when held steady on the target at a short distance will have much less effect at longer distances (and when the laser and target are both moving relative to each other).
- Official accounts of eye injuries may not be accurate unless the patient has been assessed by an expert with experience in laser eye injuries. For example, if the injury passes the six questions listed in the "Diagnosis" section of this page.
- Often the injuries are examined by persons without experience in laser eye injuries, so they are misdiagnosed. For example, a pre-existing condition may be mistaken for a new eye injury. Or given the power of lasers in the crowd, it becomes highly unlikely that any of the lasers could cause the reported injuries.
- Sometimes a person exposed to bright laser light will rub their eyes too hard. This rubbing can scratch the cornea. It is painful but it will heal. This is not directly caused by the laser light. Visible laser light passes through the clear cornea and is focused by the lens on the retina (where actual damage can occur).
We often see press reports of pilots and others where it is incorrectly claimed that visible laser light damaged a person's cornea. Actually, it is the post-exposure rubbing that caused the corneal injury.
Use and misuse of the NOHD to determine laser hazard distances
- Sometimes police or press accounts will list scientific descriptions of laser safety, such as the "Nominal Ocular Hazard Distance" or eye safety distance
For example, a very low-powered 1 milliwatt laser pointer has an NOHD of 23 feet (7 m) while a powerful 100 mW handheld laser has an NOHD of 230 feet (70 m). These non-experts will then imply that the laser light can cause eye damage 23 (or 230) feet away.
But this misstates the NOHD concept.
- First, there is actually a safety factor built into the NOHD. It is conservative, so a person could be well within the NOHD (closer to the laser) before any detectable change happens to the retina.
- Second, the NOHD is based on experiments where the laser and the target (a monkey's eye) were fixed in place at a short distance. This is not the same as in a protest situation where the laser is much further from the target (the beam has spread out) and both are moving relative to each other (further spreading out the laser beam's heat).
- Finally, the NOHD was determined based on the smallest visually detectable change to the retina. It is likely that such a small injury would not normally be noticed, or would heal just as small skin burns heal.
Under laboratory conditions (fixed laser and target at close range), at about 1/3 of the NOHD there is a 50/50 chance of causing the smallest visually detectable change to the retina. This 1/3 distance is marked ED50 in the diagram below which color-codes a laser’s eye hazard: Red is a definite hazard, yellow is a potential hazard, and green is not considered to be hazardous.
Police, pilots, the press and others should not imply that eye injuries are likely to occur at the NOHD distance. Scientists do state that, if a person must be exposed to laser light, then it is considered safe to do so past the NOHD. But they do not say that at the NOHD distance, injuries are likely to occur.
During Hong Kong protests with dozens or hundreds of lasers being aimed at officers, as of August 9 2019 only three officers received medical treatment. And this is just treatment; it is not known whether they had an actual, serious or permanent injury.
In short, even if lasers are considered as weapons, in general they are less hazardous than thrown objects, incendiary devices, guns, etc.
For more information on the NOHD and the "injury distance" ED50, see this page.
Letter: Is this webpage too lenient to protesters?
- On September 19 2019 we received this letter via email:Your page about laser pointer protests seems to be too lenient to protesters.
The power of these laser pointers brought in Hong Kong is typically from 28mW to 912mW; see https://www.customs.gov.hk/en/publication_press/press/index_id_1583.html
They aim their laser pointers at policemen within a distance of approximately 20m, sometimes more sometimes less. According to your info about NOHD, hazardous distance is 1/3 of NOHD, NOHD of 28-912mW laser pointers is 36-213m. 1/3 of NOHD is 12-70m. Those laser protests probably are within hazardous distance.
If a 20m attack at policemen with a 912mW laser pointer is not hazardous, then aiming at planes should not be an offence too.First, this is a thoughtful letter. The writer clearly read the page, did some hazard distance calculations, and had a good question.
We did write "In terms of causing eye injuries to police, in general lasers are not effective." (emphasis added). With more powerful lasers such as 912 mW, there is a possibility of injury. But here is why in general lasers are not effective in protests:
At 1/3 of the NOHD, there is a 50/50 chance of a laser beam causing the smallest visibly detectable change to the retina, under laboratory conditions where the laser is fixed in position and the eye also is not moving, if the entire beam is within the pupil of the eye.
Protest conditions are different:
- The laser is almost always handheld and the targeted person is moving relative to the beam, reducing the time the laser is on any one spot of the retina.
- Not all the laser light may go through the pupil. Protests do not take place in total darkness. It is likely the pupil is constricted to be smaller than the 7 mm diameter assumed for laser safety purposes. This means it is harder to get the entire laser beam (which does spread out) into the pupil.
- A higher-powered laser such as 912 mW will usually have a more divergent (wider) beam than lower-powered lasers, perhaps 1.5 to 2 times the beam spread of lasers with a few milliwatts. If we change the hazard distance calculator to use 1.5 or 2 milliwatts, this brings the NOHD of a 912 mW laser down to 142 or 107 meters. The ED50 "1/3 of the NOHD" then becomes 45 or 34 meters.
- Keep in mind the damage scientists found at 1/3 of the NOHD was the smallest visibly detectable change. Such a small burn may heal and may not be noticed unless it occurs in the central vision. (Small-scale laser injuries can be difficult to confirm. For example, was there a pre-existing injury? See this page for more details.)
The example earlier on this page helps illustrate these points. Police used a high-powered laser at close range on a dark ink-covered part of a newspaper. After a few seconds, smoke occurred. But later a protester held up a newspaper while dozens of lasers tried to burn it but could not according to a news story. This shows that there can be a significant difference between laboratory or controlled conditions, and real-world conditions at longer distances with handheld laser sources and targets that are unsteady, moving or can actively avoid beams.
We are certainly not encouraging persons to aim lasers at other people's head or eyes. No one should do this except under special conditions where the laser exposure is known (such as at laser light shows that use legal, safe audience scanning, which is an entirely different and complex topic).
It may be possible that with higher powered handheld lasers in a protest, a proven, documented and permanent eye injury could occur. But we do believe that, in general, lasers are not effective in terms of causing eye injuries to police.
Other protest hazards such as thrown objects, beanbag rounds, incendiary devices, water cannons, tear gas and of course bullets can cause more severe temporary and permanent injuries. For example, there is the well-known case of a woman who said she may lose an eye after being shot with a beanbag round fired by police.
The writer's final question referenced aiming at aircraft. This is a different situation entirely. Here, the laser is not an eye hazard but instead is a bright source of light that can be a distraction, cause glare or even temporary flashblindness and afterimages. This is why many countries and jurisdictions have laws specifically against aiming a laser at or near aircraft. More information is here.
Thanks to the letter writer for emailing their questions and concerns.
Ineffective ways to defend against lasers at protests
- Here are some proposals intended to reduce the number or effect of laser pointers used at protests, which are unlikely to be effective:
- Some have suggested making mirrored visors or face shields. It is expensive to coat a large expanse of plastic with a mirror coating plus protective overcoat. Even if done, the coating will reduce the amount of light coming in through the visor or shield. It would be like wearing mirrored sunglasses. In general, the more light that is reflected, the more light that does not pass through the coating.
- Because visors or face shields are rounded, mirroring will not reflect laser light back to the person holding the laser. Fortunately, the curvature will spread the light out more so a laser beam bouncing off a mirrored visor or shield would be unlikely to hurt others. If the visor or face shield was flat, then it would be reflecting the laser in a different, essentially unknown direction.
- For various reasons, putting a retroreflector on a target (e.g., an officer's helmet or clothing) would bounce some of the beam light back to the laser but would not have the intended effect of returning the laser beam's full power (irradiance) to the source.
- Making laser pointers illegal to import or own would not be effective, at least in the short term (a few years). Protesters obviously would continue using newly-illegal pointers if they felt it was effective. In countries such as Australia where pointers were made illegal due to persons aiming at aircraft, the rate of lasing aircraft actually went up significantly after the ban. And there were other unintended negative effects as well. For more information, go to the page "What should be done about laser pointers" and read the section "…but don't rely on a laser ban (alone) to prevent laser misuse".
Laser pointers vs. handheld lasers
- In the laser pointer safety field, there is a distinction between laser pointers and handheld lasers:
- The term "laser pointer" technically means low-powered handheld lasers which are legal to sell, buy and/or use for pointing purposes in a particular jurisdiction.
- Handheld lasers may look and operate like laser pointers, but they are more powerful than those legally allowed to be sold, purchased and/or used as pointers.
To give an example, in the U.S. it is illegal to manufacture, distribute or sell a laser 5 milliwatts or more as a "laser pointer" or for pointing purposes. But it is legal to manufacture, distribute or sell a handheld laser 5 mW or more as long as it has the proper labeling and safety features. (And, under federal law, anyone in the U.S. may own a laser of any power. A few states and localities may have some restrictions on laser possession.)
The reason this is important in the context of protests is that a laser pointer (defined as being less than 5 mW or 1 mW depending on the country) usually can do little or no harm to eyes or cameras. However, handheld lasers can be hundreds or thousands of milliwatts and could harm eyes and ruin camera sensors.
Since the press usually calls any handheld laser a "laser pointer", it may be futile to invoke this distinction. But the public should know that low-powered pointers like those sold for presentations and playing with pets (less than 5 mW) are relatively much safer than high-powered handheld lasers (50-2000 mW) often used in protests.
- For general laser injury news reports from LaserPointerSafety.com, see these links: aviation-related injury reports, non-aviation injury reports, other injury reports.
We have two pages describing laser beam hazards, and the possible effects and injuries; see Don’t aim at head & eyes, and If you are hit by a laser beam.
We also have an older page on the risks of lasers versus other products.
On August 8 2019, the South China Morning Post published an article, "Laser pointers are not illegal in Hong Kong, but are they weapons, and what harm can they do to people?". Most of the article is accurate, although a professor of electrical engineering did not adequately discuss the difficulty of handheld lasers causing injury in an adversarial, protest-type situation.