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| History Of Strobe Lights Used On Police Cars And Emergency Vehicles |
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The origin of strobe lighting dates back to 1931 when Harold Eugene Edgerton employed a flashing lamp to make an improved stroboscope for the study of moving objects. By the 1960’s, strobe lights began to find their way onto police cars, fire engines and ambulances. From that time on, Light Bars have since become the dominant means of drawing attention to official vehicles, as they are found on nearly every emergency vehicle and on certain other semi-official vehicles (like tow trucks) that require attention.
A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. Strobe lights have many uses, including scientific and industrial applications, but are particularly popular in night clubs where they are used to give an illusion of slow motion (“temporal aliasing”). Night club strobes first arrived on the scene in the 1970’s and have become much more popular since then. Other well-known applications are in alarm systems, theatrical lighting (most notably to simulate lightning), and as high-visibility navigation lights, as well as still widely being used in law enforcement and other emergency vehicles after nearly four decades.
Today the typical strobe lights used on police and emergency vehicles are slowly being replaced by LED technology, just as strobe lights themselves largely replaced regular halogen lighting in this application back in the 1960’s. LED lights have several significant advantages over strobe lights, including reduced power draw and greater durability.
Strobe light has also been used to see the movements of the vocal cords in slow motion during speech, a procedure known as video-stroboscopy. Other interesting uses of strobe lights include dramatic photographs of objects such as bullets in flight.
A typical commercial strobe light has a flash energy in the region of 10 to 150 joules, and discharge times as short as a few milliseconds, often resulting in a flash power of several kilowatts. Larger strobe lights can be used in “continuous” mode, producing extremely intense illumination. The voltage of strobe light systems tends to be on the high side, even though the wattage consumed may not be very high.
The light source of a strobe light is commonly a xenon flash lamp, which has a complex spectrum and a color temperature of approximately 5,600 kelvins. In order to obtain colored light, colored gels or casings around the bulb must be used.
Strobe lights and epilepsy
Strobe lighting can trigger seizures in photosensitive epilepsy, thus most strobe lights on sale to the public are factory-limited to 10~12 flashes per second in their internal oscillators, although externally triggered strobe lights will often flash as frequently as possible. At a frequency of 10 Hz, 65% of affected people are still at risk. The British Health and Safety Executive recommends that a net flash rate for a bank of strobe lights does not exceed 5 flashes per second, at which only 5% of photosensitive epileptics are at risk. It also recommends that no strobing effect continue for more than 30 seconds due to the potential for discomfort and disorientation. However, these rules pertain to indoor use of strobes only and do not apply to strobes such as those used in emergency vehicle lightbars.
Strobe lights and accidents
Many police officers have complained that the blue colored strobe lights hurt their night vision, as opposed to red lights. However, the colors of the lights are set by state law, and although consideration has been given to these complaints in many jurisdictions, this is not the case everywhere. One way in which states have been able to mitigate this issue has been through the use of lightbars that allow control of the direction in which the blue lights are activated, and also by means of revised vehicle stop procedures to let police officers safely provide support at the scene while minimizing blue strobe light exposure to their eyes during darkness. This issue has become of particular concern in those jurisdictions where LED strobes are used due to their high luminosity (brightness).
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