CAN you stop someone in their tracks using nothing but a flashing light? The US army and the Department of Homeland Security seem to think so. Both are backing the development of a new kind of weapon which amounts to little more than a powerful strobe light. Wielded like a conventional gun, this weapon is designed to trigger 鈥渇licker illness鈥� 鈥� a condition akin to severe motion sickness 鈥� which leaves the target dazed, nauseous or completely immobilised. Its developers suggest it could be just the thing for disabling armed criminals or dispersing a rioting mob. If all goes to plan, police and border guards could soon be using the weapon in earnest.
It鈥檚 a controversial prospect. Supposedly non-lethal weapons such as rubber bullets can unintentionally kill or injure and police have been accused of using these kinds of weapon indiscriminately. Will it be the same story with the flicker gun? The uncertainty is all the greater as no one can agree on the physiology of flicker illness or even whether it exists at all, let alone how effective these weapons will be and what their potential dangers are.
According to Bob Lieberman, president of Intelligent Optical Systems of Torrance, California, which is developing a device it calls the Incapacitator, flickering lights are highly effective against almost everyone. Yet evidence dating back to the 1950s suggests that fewer than 1 person in 3 will be vulnerable. 鈥淚 would be completely floored if they can do all the things claimed,鈥� says Richard Servatius, director of the Stress and Motivated Behavior Institute at the University of Medicine and Dentistry of New Jersey.
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The Incapacitator is typical of this new kind of weapon (see Diagram). Resembling a chunky flashlight, it contains a closely packed array of powerful multicoloured LEDs instead of a conventional bulb. The light they beam out is bright enough to dazzle, which in itself would make it hard for anyone held in the beam to aim a weapon. But the Incapacitator is far more than just a powerful flashlight, Lieberman says. The differently coloured LEDs are programmed to pulse on and off in a particular sequence and at a particular rate that its manufacturer claims cause disorientation, dizziness and vertigo in around two-thirds of those exposed.
Lieberman says his company has discovered one particular pattern of pulses that makes almost all people feel nauseous. 鈥淎necdotally, we have one combination of wavelengths and frequency that seems to affect just about everyone.鈥� Development of the Incapacitator is being supported by $800,000 from the Department of Homeland Security, which hopes to supply the device to security services by 2010.
The US army is after something more powerful: a strobing light capable of being mounted on an uncrewed aircraft that will target a threatening mob from a distance of hundreds of metres. Its Research, Development and Engineering Command has awarded a $600,000 contract to Pennsylvania-based Peak Beam Systems, where engineers are modifying a 15-million-candela xenon lamp, which is about 100 times brighter than a typical car headlight. By adding a strobe function and adjusting the frequency and amplitude of the light pulses they plan to produce a device that will immobilise anyone caught within the beam. According to the company鈥檚 sales director, Will Harcourt, tests of the device by the Office of Customs and Border Protection based in San Diego, California, showed that people were 鈥渋mmobilised and falling down at 500 yards plus鈥�.
Charge of the light grenade
At the other end of the scale, the Jade 鈥済renade鈥� made by Nanohmics in Austin, Texas, is designed for use in enclosed spaces. About the size of a soft drinks can, this device is claimed to be an alternative to the stun grenades that troops and police throw into a building to incapacitate those inside before storming it. Unlike conventional stun grenades, which use explosives to create the flash and bang, and so can injure people or start fires, the Jade grenade uses powerful LEDs operating at a wavelength of 520 nanometres, near the peak sensitivity of human vision. They can be programmed to generate either a single intense flash or a continuous strobing pattern that company co-founder Mike Mayo says triggers symptoms including dizziness and even epileptic-like seizures. 鈥淚t鈥檚 like 鈥榞et me outta here鈥�,鈥� he says. 鈥淭he effects go beyond what is in the current literature.鈥�
If these weapons live up to their designers鈥� claims, they could provide an effective way to disarm criminals or disperse rioters without causing serious injury. But do they? Can a flashing light reliably immobilise someone, and how likely is it to cause lasting harm to those it is used against 鈥� or any bystanders?
Certainly, exposure to lights flashing at frequencies anywhere between 2 and 60 hertz has been found to trigger a range of symptoms, stretching from mild headaches and muscle spasm to convulsions or epileptic seizures. These effects were investigated in the 1950s, after helicopter pilots reported that sunlight shining through whirling rotor blades left them feeling dizzy and confused. In subsequent experiments, volunteers were exposed to lights flickering at between 2 and 30 hertz. Of 306 subjects, around a quarter experienced either headaches, nausea or a sensation of movement similar to vertigo. Sixteen 鈥� about 5 per cent 鈥� fainted or experienced convulsions typical of epilepsy, even though they had previously shown no signs of the condition.
Since then it has been found that TV pictures can trigger similar seizures in people with no history of epilepsy. In 1997, some 700 children experienced seizures while watching an episode of a Japanese 笔辞办茅尘辞苍 cartoon that featured coloured lights flickering at around 12 hertz. Ten years later, a flickering logo in a TV advert for the 2012 London Olympics induced seizures in around 30 viewers. Even TV images without obvious flashing lights can trigger the effect, most likely due to the 50-hertz flicker from the cathode-ray tube or from the 25-hertz screen refresh rate.
鈥淚n 1997, 700 children experienced seizures while watching an episode of a Japanese 笔辞办茅尘辞苍 肠补谤迟辞辞苍鈥�
Large-scale studies on flicker illness in otherwise healthy people are thin on the ground, however, according to Jeremy Cushman at the Department of Emergency Medicine at the University of Rochester Medical School in New York. Cushman and Douglas Flocarre from the Maryland Institute for Emergency Medical Services Systems in Baltimore wrote a review of flicker illness that was published last year (). They estimate that around a quarter of those exposed to flashing lights experience symptoms such as headaches or vomiting, and that only around 1 in 5000 experience severe responses such as light-induced epilepsy 鈥� a significantly smaller proportion than reported in the 1950s study 鈥� but they also suggest that milder symptoms may often go unreported.
Some neurologists, including John Hastings, president of the US Aerospace Medical Association in Alexandria, Virginia, are deeply sceptical of the notion that flashing lights can have any profound influence on the brain. He suggests that for the majority of the population, the incapacitating effect of a bright flashing light would be trivial 鈥� no worse, perhaps, than being dazzled by oncoming headlights or driving with the sun in your eyes. 鈥淚ncapacitating in a sense, yes, but without abnormal brain activity of any kind.鈥� Only people with epilepsy will be seriously affected by flickering lights, he says.
Flight simulator
Apart from those vulnerable to epilepsy, a few people 鈥� perhaps 3 in 1000, according to available studies 鈥� might experience what鈥檚 called the photomyoclonic response which usually involves spasms in facial muscles. While this might be uncomfortable, Hastings says it is 鈥渁 benign condition of no significance鈥�. In his view, the term 鈥渇licker sickness鈥� should probably be discarded. 鈥淚t does not exist in the neurological scientific community, at least not in contemporary literature.鈥�
So could devices like the Incapacitator be tapping into a different mechanism from that documented for flickering light? The dizziness and nausea sometimes experienced by people using computer-based flight simulators are seen by some as offering a clue. This 鈥渟imulator sickness鈥� arises because the brain uses two sources of information to detect whether the body is moving relative to its environment: the eyes, and the semicircular canals and gravity sensors of the inner ear. When these give contradictory signals 鈥� if you sit staring at a magazine in the back of a moving car, say 鈥� then nausea and headaches can follow.
Much the same thing happens when someone is concentrating on a flight simulator screen, so could flashing lights trigger a similar effect in the brain? Not according to Rollin Stott, principal medical officer at the Centre for Human Sciences in Farnborough, Hampshire, UK, which is operated by the military technology company Qinetiq. Stott says there is no direct correspondence between simulator sickness and the effects of flickering light. 鈥淲ith flicker there is no motion, either real or implied,鈥� he points out
The possibility remains that certain light wavelengths and pulse frequencies are particularly effective at targeting the brain, or that the shape and rise time of the pulses is important. For example, Peak Beam Systems鈥檚 strobe lamp uses light pulses based on a square wave, which might explain why it seems to cause effects not observed with other strobes at the same pulsing frequency.
Aside from the physiological effects of strobing, Harcourt says his company is interested in the behavioural influence of the technology. Does it alter a pattern of action, say? 鈥淚t is important to keep the objectives of the technology in mind: determining threat levels based on reactions to the strobe, altering the direction a person or a vehicle is moving or disrupting small groups of people.鈥�
The effectiveness of one device 鈥� the Incapacitator 鈥� is due to be tested at the Institute for Non-Lethal Defense Technologies at Pennsylvania State University, but details are likely to remain secret until the weapons are used for real. That鈥檚 unfortunate, says Cushman. If the developers of these weapons have data on their ability to reliably induce seizures, they should publish it, he says. 鈥淚t would be valuable to the scientific community to share that, as it may further define the physiology behind such a response.鈥�
鈥淚f the developers of these weapons have information about their ability to reliably induce seizures, they should publish it鈥�
So should the weapons be used in public without independent testing? And what about reflections from buildings with coated glass windows, or from metal structures which could focus the light beams to dangerous levels? Lieberman says the Incapacitator is fitted with a rangefinder that reduces its power if targets are too close. And Ley Sander, a neurologist at University College London, says the risk to people with photosensitive epilepsy will be minimised if the devices operate at pulse rates above 25 hertz. Seizures produced in people who do not have epilepsy should not have any long-term neurological consequences, but that does not mean they are harmless, he warns. Anyone with a weak heart could be in danger, he says.
Steve Wright at Leeds Metropolitan University in the UK, who studies the technology of political control and counter-terrorism, says strict safety standards should be applied to this kind of weapon. He is not optimistic that this will happen, however. 鈥淎 lack of physiological and biomedical knowledge of the effects of crowd-control weapons has not much hindered weapons manufacturers and government security forces deploying dubious crowd control weapons in the past,鈥� he says.
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