The various options of police car lights
This article discusses the development of the blue and red flashing lights commonly used as police car lights and signals on the roof of police cars.
The history of police car lights is a long one and new developments are continually coming onto the market. Originally police cars did not have or use special lights. If marked at all a shield was painted on the door. Pretty soon it was realized that a police car needed to distinguish itself so they were fitted with sirens. The trouble with sirens is that they alert other road users to the police’s presence but does not immediately distinguish where the noise is coming from. A blue lamp had been the sign for a police station for centuries, so a single blue light was put on the cars roof to distinguish the police cars lights for other cars lights.
Because the light was still it helped but it was soon realized that a constant light is not as visible as a flashing light. Flashing lights work well but incandescent lights deteriorate and burn out fairly quickly if they are constantly flashed. The Police beacon was developed which was a single incandescent light in a blue dome. Rotating around the light was a motor driven mirror reflector which directed a beam of blue light to swing around the beacon. From afar it looked exactly like a flashing light and was very visible. This beacon became the standard for all emergency lights on all vehicles so ambulances had a red beacon and service trucks had an amber one. The blue police car lights were standardized on one or two blue beacons. Illumination and visibility were improved with the replacement of incandescent with halogen lamps.
The appeal and success was very apparent. The more police car lights flashing and the more noise it made the better. So the Lightbar was developed. Initially a Lightbar was a flat bar mounted across the roof of a police car. Onto this was mounted 2 rotating beacons side by side. Then they added a white or a red light to shine onto an incident and pretty soon the idea of a blue and a red flashing light mounted on the roof of a police vehicle became standard. A further development came when it was realized that the aerodynamics would be vastly improved if the whole array was encased is one cover so and entire integrated lightbar was built and marketed as a single unit. The actual standards vary from jurisdiction to jurisdiction. But generally police car lights nowadays include a light bar with and array of red and blue flashing lights. In some police authorities there is a white element facing forward but no white light will ever shine backwards.
Then came the development of the LED. The LED is a wonderful invention as it is electronic and the light emitted is not due to resistance in a filament but into the passing of an electron from high to low potential though a “gateway”. Incandescent lights generate heat (90% of the energy used in lighting, be it incandescent or halogen, is heat). LEDs are solid state so have nothing to break or shatter and are very reliable, typically lasting thousands of hours and almost certainly outlasting the life of the police car. Initially they were low power but over the last 10 years have increased in power output. It is found that if they are mounted in clusters they can be grouped according to color and are an effective replacement for the old type of moving police car lights.
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