There are a few reasons for this - some reasons have been guessed, some are very practical theories. The main reason that police vehicles use lights is to draw attention and to show where an oncoming vehicle is arriving from.
While a siren may initially command the attention of people nearby, the sound is often refracted by surrounding buildings, making it difficult to work out where the vehicle is and how quickly it is moving.
Adding police lights to vehicles means that people can see as well as hear where a vehicle is coming from. This means that the vast majority of people will be alerted to the presence of an emergency vehicle in some way. With technology these days, everything from roof mounted light bars, to visor light bars , are easily visible when flashing.
Police cars use lights in a variety of different ways. Some patterns of flashes may be used to warn traffic that a car is approaching, particularly when nearing a junction.
Other patterns may be used to indicate a parked police car at a crime scene and there is a theory that some patterns and colors are used specifically to attract the attention of other officers. To begin with, the police car light bars were not colored but were simple white spotlights. The other problem was that these lights required a lot of battery power. Strobing red lights were introduced in the s and by the s, most police cars traveled with a single beacon.
The reason for the red beacon seems to be that most people associate the color red with danger and the instruction to stop. Across the country, all red signs indicate danger ahead a flashing red light is difficult to ignore and so most people would take heed of a passing police vehicle. They can be used to warn of a potential danger, for example if a car is broken down or has been pulled over at the side of the road.
Without the presence of the strobe lights, cars that have been pulled over in the dark would be difficult to spot by other road users and could potentially cause accidents. During police chases, the LED emergency vehicle lights are used to warn others to stay out of the way, and the lights might be used to warn of the presence of the car itself — for example, if a police car has to stop in a hazardous position, they will usually operate the strobe lights in order to warn other drivers that the car is there.
There are other types of light used by police. An LED light bar inside the car might be used by undercover or plain clothes police.
These are difficult to spot in an unmarked vehicle, and they allow the police to remain invisible until required. Small portable and rotating lights serve a similar purpose and are usually placed on the dashboard before the car sets off. Another spotlight may be positioned near the door window, which officers can use to illuminate a scene, vehicle, or pedestrian, especially at night when lighting levels are low.
The aim of LED strobe lights is to alert people to the presence of police. In most cases, this is done so that other road users are aware of the hazard that they pose.
The sudden appearance of these lights can be alarming, but they do serve a genuine purpose. Generally, it is the responsibility of the police to avoid other traffic, but it is also the responsibility of drivers to move over to the right hand side of the road in order to let the police and other emergency vehicles pass. Officers also use these lights while their cars are parked for police incidents that are in progress — for example, a vehicle traffic stop or domestic disturbance at a residence.
Approaching police lights warn civilians to move out of the way and to avoid police activity scenes. Each bright color is different and defines a certain situation. Light bars have at least two colors. Red lights signify an immediate emergency. Blue lights define police presence and can be spotted easily from a great distance. White lights are used by night-shift officers to brighten dark areas or to shine on suspects who are traveling on foot or being interviewed.
Yellow lights warn approaching vehicles that patrol cars are slowing down or parked on busy roads. All lights may be used at the same time.
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