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Why are Police Lights Red and Blue?

Thursday, July 13, 2017
Julie Adams

Have you ever wondered why police cars use red and blue lights? The answer is partly historical and partly practical. Over the years, changes in law enforcement, technology and energy efficiency have all affected the evolution of police lighting.

In the 1940’s, most police departments used a simple beacon light mounted atop their patrol units or a single non-flashing, red light at the front of the car. The choice of red most likely originated from the color red being associated with “stop” and other warning signs across the country. Over time, emergency vehicles began to incorporate the latest high-tech flashing lights. They also began to add blue lights to their fleet. So why red and blue?

It's difficult to pinpoint exactly why this color combination became the most popular, since usage and regulations vary greatly from state to state. However, there are several common theories about the origin of this lighting trend. While red is meant to alert drivers, red lights can also get overlooked in traffic since most vehicle tail lights are red. Some studies indicate that red lights are more visible during the day, while blue lights are more visible at night. The combination of flashing red and blue lights helps to alert drivers regardless of the time of day.

Interestingly, some experts also say that using both red and blue lights mitigates problems associated with drivers who are colorblind. Those who have may trouble seeing red often have no trouble seeing blue. Conversely, drivers who have trouble seeing blue can often see red. Red has the longest wavelength, meaning it will disperse less and can more easily reach the eye, even in foggy conditions.

Police vehicles need to gain access to incidents as quickly as possible, and effective lighting helps make this possible. Advances in lighting technology in the early 1990s saw the rise of popularity of emergency light bars. Around the same time, police also began using LED lights that were more energy efficient than their previous flashing bulbs. Today, LEDs offer many brilliant red and blue lighting options, flash patterns and programmable features for each department’s specific needs.

Emergency lights have come a long way over the years. Although these red and blue lights still serve the primary purpose of visually conveying an emergency vehicle’s presence, they can also serve as scene lighting and traffic control. Today’s light kits can integrate with control units to produce dozens of high-tech light and siren combination patterns. Whether it’s on a patrol car or an ambulance, having a powerful package of red and blue LED lights is an essential part of an emergency vehicle’s effectiveness and safety.