Our Technology: StunRay® The Visible Light Stun Effect
StunRay® The Visible Light Stun Effect
What is the Visible Light Stun Effect?
The visible light stun effect is a temporary large reduction in visual sensitivity due to neural overload, in response to a sudden change in applied light. It is a particular case of light adaptation, which is the process by which the eye adapts from a low intensity of applied light, to a high intensity of applied light.
Called the StunRay®, the effect has been described as being hit with a barrage of overpowering “light-bullets”. It is similar to, but more intense than, what occurs when a person is exposed to a camera for flash photography.
What is Visible Light?
Visible light is broadband incoherent optical radiation. It is electromagnetic energy in transit, and is said to be propagated through space by photons that are conceptualized to be elementary particles with zero mass and zero electric charge.
The photon is defined to be the quantum unit of light that exhibits both particle-like and wave-like properties. As a particle, a photon is characterized by a quantum unit of energy hv , where h = 6.6 x 10-34 J-s is Plank’s constant, and v s-1 is a frequency. As a wave, a photon is characterized by a wavelength λ nanometer (nm). If the wavelength is less than 100 nm, the radiation is said to be ionizing. If the wavelength is greater than 100 nm, the radiation is said to be non-ionizing.
Frequency and wavelength are related by u = cov λ/n is the speed of the propagation of the energy, co ~ 3 x 108 meters per second is a constant, and n is an index of refraction that characterizes the properties of the medium in which the energy is propagating.
Radiation with wavelengths between 100 and 400 nm is called ultra-violet (UV) radiation. Radiation with wavelengths between 400 and 700 nm is called visible light, or just light, as shown in Figure 1. Radiation with wavelengths between 700 and 1400 nm is called IRA infra-red radiation, between 1400 and 3000 nm is called IRB infra-red radiation, and between 3000 nm and 1 millimeter is called IRC infra-red radiation.
Figure 1. Radiation
In the case where the radiation consists of waves of varying wavelengths with random, uncorrelated phase relationships, the radiation is also said to be broadband, and incoherent. The sun and artificial sources of light such as incandescent light bulbs, arc lamps, and fluorescent lights produce broad band incoherent optical radiation. Artificial sources of broad band incoherent optical radiation produce negligible IRC.
In the case where the radiation consists of waves with identical phases, the radiation is said to be coherent. Lasers produce coherent optical radiation, including IRC.
What is Photoreception?
Photoreception occurs in the retina, where light receptive pigments absorb the applied light, and trigger chemical reactions. The chemical reactions result in nerve impulses, which are then processed and perceived as an image.
The retina is an extension of the brain, and is the receiver that converts the energy of the applied light into electrical signals. It is located at the back of the eye, and contains blood vessels, ganglion cells, bipolar cells, rods and cones, in that order, and in the direction of the propagation of the applied light. Approximately 125 million rods and 7 million cones are located underneath a layer in the retina that contains the ganglion and bipolar cells. Those cells provide the interconnections between the rods, cones, and the optic nerve. The optic nerve has approximately 1 million fibers.
The retina is backed by the pigment epithelium layer and the choroid, which is a spongy tissue, with large vascular blood vessels. It appears that the primary function of the choroid is to maintain a relatively uniform temperature of the eye in general, and the retina, in particular.
The rods provide night vision. They are cylindrically shaped structures with a characteristic diameter of 2 μm, and are non-uniformly distributed throughout the retina, with wider spacing toward the periphery of the retina.
A single photon absorbed by a small cluster of adjacent rods is sufficient to send a signal to the brain. However, since a single rod may be connected to multiple ganglions, and multiple rods may be connected to a single ganglion, the brain cannot determine exactly where on the retina a single rod is, and the resulting night vision image is not sharp.
The ones provide day vision. They are cone shaped structures. In the fovea, they have a characteristic diameter of 1.0 to 1.5 μm, and a spacing of 2.0 to 2.5 μm. Since in the fovea there is one cone per nerve fiber, the resulting day vision is sharp, and includes color differentiation.
When the eye is dark adapted, the rods are active, and the cones are not. When the eye is light adapted, the cones are active.
The ganglion cells have a response that is primarily determined by stimulus contrast, which is a change in applied light, rather than by the previously-occurring light adaptation. They are the last neurons in the retina, and have axons that project up to the brain.
Both the rods and cones contain visual pigments. The pigments consist of an opsin, which is a protein, and retinal, C20H28O, which is a hydrocarbon module that is one of the three primary forms of vitamin A.
Rhodopsin is the light-absorbing rod pigment. It absorbs the electromagnetic energy of the applied broadband optical radiation at most visible light wavelengths, as shown as the dashed black line (R) in Figure 2. Since rhodopsin most strongly absorbs green-blue light, it appears to be reddish-purple, and is also called visual purple.
Figure 2. Absorption spectra
Photopsins are the light-absorbing cone pigments. There are three. Each is composed of a unique opsin, and retinal, and each absorbs unique band of the visible light wavelengths, as shown in Figure 2. Photopsin I, II, and III have peak absorptions at long (L) yellow-red, medium (M) green, and short (S) blue-violet wavelengths, respectively. This is how color is perceived.
The rhodopsin and the photopsins are the first chemicals in the sequence that converts the applied electromagnetic energy into electrical signals. In the absence of applied light, the retinal is in what is called an 11-cis configuration, which has a kink, and is covalently bonded to the opsin. In response to the application of light, the energy provided by the absorbed photons causes the retinal to twist about a carbon double bond, and straighten out into what is called an all-trans configuration, as shown in Figure 3. This change in the physical configuration of retinal is called isomerization, and is the basis of photoreception.
Figure 3. Isomerization of retinal
After the retinal isomerizes, it no longer fits into the opsin bonding site, and as a result, the pigments split into their respective opsins, and retinal. This is called bleaching. The bleaching, in turn, starts a sequence of electro-chemical reactions that ultimately ends with the perception of an image. The first chemical reaction occurs within seconds after the application of the light. If light is continuously applied, the rods and cones are in a steady state in which the rates of bleaching and regeneration of visual pigments are equal.
How does the StunRay® work?
To invoke the stun effect, a white light from a short-arc lamp is suddenly applied to the eyes. In response, all of the visual pigments are bleached nearly instantaneously, and become temporarily unresponsive. As a receiver, the retina is said to be desensitized.
Since a number of chemical steps are needed to complete the bleaching, an electrical change occurs in time well before the actual bleaching. A flood of electrical signals is produced while the retinal neurons adapt, and since the dynamic range of the neurons associated with vision is limited to about 101.5, which is much less than the 1014 dynamic range for luminance, the retina, as a receiver, is said to be saturated. The resulting perceived image is uniformly white, and, as a result, the person is unable to discern his or her immediate surroundings, has a natural tendency to stop physical motions that require gross motor skills, including walking, running, or other aggressive movements, and is said to be stunned, dazzled, or temporarily incapacitated. Some have described the effect as a visual concussion. Figure 4 shows the condition of a stunned person during and immediately after the application of the light.
Figure 4. The stun effect
Since the retina has no pain receptors, the stun effect is painless.
What is the typical recovery time?
The recovery from stun effect is process by which the retina receive sensitivity is restored. It is a particular case of dark adaptation, which is the process of adapting from a high intensity of applied light to a low intensity of applied light. It is similar to what occurs when a person walks into a completely darkened room at night, from a room that is lit.
When the eye is light adapted, the cones are active, and the rods are not. If the external light is suddenly removed, the resulting perceived image is uniformly black, because the cones function poorly in low light, and the rods are not yet adapted, because the visual pigments have been bleached out due to the bright light.
Once in the dark, the visual pigments regenerate. The all-trans retinal is reduced to all-trans retinol, a second form of vitamin A, and travels back to the retinal pigment epithelium to be oxidized back into 11-cis retinal. The 11-cis retinal then travels back to the rod outer segment, where it can again be bound with an opsin, which increases the retina receive sensitivity.
Figure 5 shows the dark adaptation response. The horizontal axis is time, in minutes. The vertical axis is the retina receive sensitivity, expressed as the logarithm of the magnitude of the luminance of the applied light, in micro-micro Lamberts (µµL), where one Lambert is candela per square centimeter, and where 1 candela is 1 lumen per steradian. The shaded area represents 80% of the population. Adaptation consists of two parts. One, which is fast, is due to neural response. The other, which is slow, is due to the regeneration of the visual pigments. Full adaptation can take up to 30 minutes.
Figure 5. Dark adaptation response
Since the recovery from the stun effect is a particular case of dark adaptation, Figure 5 is an estimate of the time needed to fully recover from the stun.
Is the StunRay Safe?
Yes, when used properly. The intensity and duration of the applied light must be high enough and/or long enough to cause the stun effect, yet be low enough and/or short enough to cause no injury or irreversible damage, so that the effect is fully recoverable.
Injuries to the eye and skin due to exposure to broadband incoherent optical radiation depend on the magnitude of the absorbed radiant energy per unit volume of tissue, and may be either thermally or photo-chemically caused.
Thermal injuries are characterized by burns that result in tissue coagulation, protein denaturation, and/or enzyme inactivation.
Photo-chemical injuries are characterized by a scotoma, which is a yellow lesion or scar on the retina, and are called photoretinitis, solar retinitis, or eclipse blindness. The injury may result from an exposure to an extremely intense optical radiation for a short time, or to a less intense optical radiation for a longer time. This characteristic is called reciprocity, and distinguishes a photo-chemical injury from a thermal injury. Since, at zenith on a clear day, the luminance of the sun is cd/m2, which is more than one order of magnitude greater than the upper limit of 108 cd/m2 for the cones, a photo-chemical injury may be caused by looking directly into the sun.
Laboratory studies suggest that photo-chemical injuries are due to absorption of the admitted radiant energy by the pigment epithelium and choroid. The rods and cones absorb only about 5% of the admitted radiant energy. The pigment epithelium, which is a 10 µm thick layer of tissue that is located posterior to the rods and cones, absorbs about 50% of the admitted radiant energy. Since the absorption takes place in 1 µm diameter melanin granules that are distributed within a 3 to 4 µm thick layer within the pigmented epithelium, it is that layer that is the thermally limiting structure. The balance of the admitted radiant energy is absorbed in the choroid.
What are the Exposure Limits?
Exposure limits for thermal injury are based the heat transfer characteristics of the eye structures, and on physiological studies of involuntary eye movements. The limits are intended to prevent burns by limiting the maximum temperature in cornea, lens, and retina to 37 oC to 45 oC. The irradiance needed to cause those temperatures depends on the initial ambient temperature of the retinal tissue, the magnitude and duration of the applied irradiance, and the diameter of the image on the retina.
Exposure limits for photo-chemical injury are based on animal experiments for both corneal and retinal effects, and have been corroborated for the human eye from accident data.
The International Commission on Non-Ionizing Radiation Protection (ICNIRP), and the American Conference of Governmental Industrial Hygienists (ACGIH) have defined and published limits for the exposure of humans to broadband incoherent optical radiation. The limits of the two organizations are consistent, and are intended to provide a quantified technical basis for the protection of the general public from the potentially injurious effects of exposure to broadband incoherent optical radiation.
The ICNIRP limits are internationally recognized, and are intended to provide an adequate level of protection against known photo-biological hazards under all normal exposure conditions. Limits are defined for exposure durations between 1 nanosecond and 30 kilo-seconds (8 hours), and for broadband incoherent optical radiation with wavelengths between 380 and 3000 nanometers.
The ACGIH limits are United States recognized, and are expressed as Threshold Limit Values (TLV’s), which are recommended values that should not be exceeded so that exposures that are hazardous to the general public are minimized as much as possible.
The United States Food and Drug Administration (FDA) has defined optical safety regulations for lasers and selected ultraviolet-emitting lamps, but does not have regulations for general broad-band incoherent sources of visible light. Recently, the FDA approved the use of a laser dazzler for local law enforcement and Coast Guard use.
Since the application of incoherent light (that is, broadband optical radiation) to the eye for a short duration of time does not result in the mechanical disruption of tissue in the way that the application of coherent light (that is, a laser) for a short duration of time may, the use of incoherent light photons as the ammunition for a non-lethal weapon is inherently safe.
Additionally, the human eye is naturally adapted to protect itself against sudden changes in applied incoherent light, in five ways.
First, since the rods are activated by luminances between 10-6 and 101 cd/m2, and the cones are activated by luminances between 10-2 and 108 cd/m2, the retina has a dynamic range of 1014 cd/m2, and, as a result, is inherently able to accommodate extremely wide variations in applied incoherent light.
Second, a sudden change in applied light results in an involuntary contraction of the pupil. This contraction, which occurs within about 20 milliseconds after the application of the light is called myosis, and is more pronounced when the fovea and the macula are illuminated. The involuntary contraction limits the amount of admitted energy, to protect the lens and retina from both thermal and photo-chemical injury.
Third, a sudden change in applied light results in an involuntary closure of the eyelid. Unless a person is otherwise impaired, for example, by drugs, this natural aversion response limits the duration of an exposure to a sudden change in applied light to less than 250 milliseconds, and protects the cornea, lens, and retina from both thermal and photo-chemical injury.
Fourth, a sudden change in applied light results in an involuntary movement of the head. This movement distributes the energy of the applied incoherent light to an area of the retina that is larger than the optical image, and further protects the retina from thermal injury.
Fifth, the bleaching of the visual pigments in response to a sudden change in applied light is an involuntary response, and is the way that the eye naturally protects the rods and cones from overstimulation, to the extent that it can.
StunRay® XL-2000 Non-Lethal Weapon Trials
Human subjects have been exposed to the broadband incoherent optical radiation produced by the StunRay® XL-2000 in trials. In every case, the subject was instantaneously unable to discern his/her immediate surroundings, and, as a result, stopped aggressive physical motions that require gross motor skills, and then recovered, within minutes, to his/her pre-exposure condition.
Extensive clinical evaluations by board certified ophthalmologists of the subjects after the exposure have shown that their eyes were uninjured, and that there were no permanent structural or functional changes to their eyes or visual system.
The results of the analysis, trials, and post-exposure evaluations confirm that the operation of StunRay® XL-2000 hand-held high-intensity spotlight is consistent with the ICNIRP guidelines, and may be safely used as a light-based non-lethal weapon.
These conclusions have been independently validated by David Sliney, PhD, an industry recognized optical safety subject matter expert who is a member of the Standing Committee IV, Optical Radiation, of the International Commission on Non-Ionizing Radiation Protection.
Our intellectual property is protected by design (7,497,586) and method (7,866,082) patents issued by the United States Patent & Trademark Office (USPTO) in 2009 and 2011, respectively. The patents also include European PCT filing rights.
The method patent, which was featured in the April 2011 issue of Scientific American, includes a broad claim for providing a high intensity incoherent light beam emitting device, where the device has a short-arc lamp, aiming the device at one or more target individuals, and then activating the device to produce a light beam that incapacitates the individual(s). Since a short-arc lamp is not only the closest possible practical implementation to an ideal point source of visible light, but also the highest possible performance source for applications that require projecting a tightly focused collimated beam of incoherent visible light for relatively long ranges, the patent provides Genesis Illumination with a 20 year sustainable advantage over all possible competitors of incoherent light-based non-lethal weapons, who are now restricted to use lower performance light sources.
A continuing patent application with 10 additional claims was submitted to the USPTO in January of 2011, and is pending. These claims will help to ensure that the performance of our next generation products continues to stay ahead of the competition.
The StunRay technology is both modular and scalable, to enable the rapid development of non-lethal or less-lethal weapons that are optimize for specific end uses. For example, multiple StunRay sources may be arrayed and mounted to vehicles, ships, or fixed sights to provide a non-lethal or less-lethal capability to give first responders a true long range, continuously variable, and pain-free choice between shoot and don’t shoot, at greater stand-off distances than other currently available non-lethal or less-lethal weapons. And, since the StunRay “bullets” are photons, the weapon does not require periodic reloading of physical ammunition.