The main parts of the human eye

2009 HowStuffWorks

LED Incapacitator Effects

­

T­he LED Incapacitator (LEDI) uses bright, short pulses of light to disorient the subject. Law enforcement officers have used strobe lights before. The LEDI is unique because it pulses in different colors (red, green and blue), spatial patterns, frequencies and intensities. The combined effect of the different colors and patterns temporarily blinds, disorients and nauseates the subject but doesn't cause any damage. The feeling of disorientation lasts for a few minutes, long enough for the suspect to be subdued. The LEDI has even been called the "puke ray" because of the nausea it causes.

How does strobing disorient a person? It helps to know how we process visual information. The lens of your eye focuses an image of the world on the retina, a dense collection of light-perceiving cells called photoreceptors. Once the image is taken and converted to an electrical impulse, the optic nerve transmits it to the brain's visual cortex, which interprets the pictures. The brain has a limited rate or frequency by which it can receive and process visual information. If visual information arrives faster than the brain can process it, then the person becomes temporarily incapacitated. The frequency required to overwhelm the brain is about 7 to 15 hertz [source: Rubtsov].

Strobing disrupts the flow of the visual information in two ways. First, the brightness of the strobe's flash creates afterimages in the brain. If you look at a bright light -- please don't choose the sun -- and then close your eyes, you'll "see" an afterimage of the light. Second, the frequency of the flashing hovers near 15 hertz and impairs the brain's ability to process visual information, which produces disorientation and nausea. Once the LEDI is turned off, the nausea lingers for a few minutes as the brain recovers.

Law enforcement officials don't have to shine the strobe directly in the suspect's eyes. They just have to illuminate the target so that some of the flash points are near the suspect's eyes [source: Rubtsov].

Let's see how the LEDI works.