If you work traffic stops as a patrol officer, it quickly becomes apparent that the biggest threat to your safety isn’t necessarily the occupants of the violator vehicle; more frightening are the inattentive drivers passing by. One would think the addition of patrol vehicle markings and emergency light systems would be effective in providing advance notice to approaching motorists that you’re stopped in front of them. Unfortunately, that isn’t the case.
While stopped during regular patrol duties (e.g., the execution of traffic stops, the investigation of minor and major traffic collisions, traffic control duties, debris removal and other law enforcement related activities), marked police vehicles are frequently struck in the rear by civilian vehicles. Fortunately, a solution exists: A reliable technology that begins by exciting a lot of electrons in a very small space and ends with a spectrum of very bright light.
This technology is the LED, or light-emitting diode, and it presents numerous advantages over incandescent and strobe-lighting options. I’ll detail those later, but, first, let’s look at what an LED light is and how it works.
Atom, Atom, Give Me Lots of Atoms
An LED is a solid-state object that produces light when energy passes through it. A diode is a form of semiconductor, which means it can conduct current. It comprises two types of negatively and positively charged materials. When no current is applied, each side essentially holds its own. But when you apply current, the negatively charged atoms essentially cross over the semiconductor and “invade’’ the positive side. In doing so, the negatively charged atom must release some energy. This energy, or photon, is more commonly known as light, the color of which can be determined by varying the gap between the two sides. In some cases, the gap is very small, resulting in infrared wavelengths (think about the remote for your TV). In others, the gap is larger, and the frequency wavelength enters the visible spectrum. Add more electricity, get more photons and voilá —one bright, compact light source.
Manufacturers of LEDs harness this light and direct it by refracting the light within a tiny plastic bulb in which the diode is encased. As the light refracts forward, it’s channeled toward the top of the bulb. This is why LED bulbs can direct such intense light in one direction and don’t rely on reflectors, as incandescent or strobe bulbs do.
Diodes are among the simplest types of semiconductors and are very efficient, because all of the electricity being applied goes toward the production of light. With no filament or moving parts to worry about, they’re also durable and vibration-resistant. So how do LEDs compare to
incandescent and strobe bulbs?
Feel the Heat
Ever buy one of those portable halogen shop lights for your garage? You bring it home, turn it on, light up the world and watch your electric bill climb faster than the national debt, not to mention the ability it gives you to barbeque chicken on the face of the lens. This is because incandescent bulbs have a filament in them that has to be heated to produce enough temperature to create visible light. In essence, the same process of photon release occurs in an ordinary lightbulb as in an LED, but at much higher temperatures. So high, in fact, that a typical lightbulb filament runs at about 4,000° F, which is what’s necessary to produce enough photon release to generate visible light. Because of this, most metals would instantly melt, but tungsten doesn’t, so it’s used for the filament. The catch : Tungsten catches fire at that temperature if it reacts with a combustible gas, such as oxygen, so the bulb is filled with an inert gas, such as argon. Crack the bulb, and instant combustion results when oxygen meets an extremely hot filament, causing a mini-explosion and blown bulb.
The introduction of halogen-filled bulbs meant that a much smaller bulb could be used because halogen allowed a higher temperature and a whiter light using less space, but all of this takes lots and lots of power that your vehicle’s electrical system needs to run other vital equipment, such as radar units, MCTs, in-car video, LPR and the like.
By contrast, LED bulbs use the greatest portion of energy for light transmission, so very little is wasted. This means an LED bulb draws much less energy than other choices. For example, a 9 watt LED bulb can perform as effectively as a 60 watt incandescent bulb and produce a whiter light. It does this with much less heat because there’s no filament to heat up. In fact, the temperature is so much lower that plastic is used for the bulb construction.
Another amazing advantage of the LED is that it’s self-contained in a very tiny space and can still produce a tremendous amount of light with little or no reflector needed. This is because, again, the light produced by the diode is refracted within the plastic bulb itself and the diode is very efficient.
By contrast, traditional strobe and incandescent setups require external reflectors to direct the light. This means the application in patrol vehicles is limited, and performance suffers as reflector size decreases. Yes, intensity can be increased in the form of more powerful bulbs (read: sucks power), but the problem is that tremendous heat builds up inside the lighting unit, and because there’s no air flow, the bulb lives a short life. LEDs don’t have these issues. They run cool and can pretty much be mounted anywhere because the amount of space required isn’t much more than the LED diode itself. Manufacturers add small reflective areas around each LED to direct any light that might “spill’ out the sides of the bulb housing, but that’s minimal. The end result is flexible mounting options.
In the Phoenix area, many Chevrolet Tahoe PPVs, outfitted by the Phoenix and Chandler police departments, the Arizona Department of Public Safety and others, feature strips of LED warning lights in the gap between the rear hatch and bumper. The same goes for behind the front grill where space is tight in front of the radiator. By using these strips they can dramatically affect the visibility of the vehicle without running into space issues or dramatically impeding air flow to the radiator. The same goes for visibility issues on windshield-mounted LED strips, mirror lights and intersection warning setups. The flexibility of LED choices is so great that there’s no reason not to integrate them into your patrol car lighting setup.
Another advantage of a smaller LED “footprint” is that overhead light bars can be much thinner, thereby increasing fuel economy and reducing wind noise. Some may chuckle at the second issue, but if you work the highways with a loud light bar whooshing above your head, it can wear on you. So size makes a difference, and, here, smaller doesn’t mean weaker.
Where’d Who Go?
One of the coolest things about LED lighting in law enforcement is that you can appear to be invisible one second, but then pop out in a blaze of red and blue glory the very next. This is because LEDs have the distinct advantage of being colorless when not activated. When no current is flowing, the positive and negative electrons essentially play in their respective sandboxes. It’s only when electricity flows that the light is generated, and only then is the desired color apparent. This benefit is awesome for undercover work, and it has the advantage of a slick-top without giving up illumination or emergency lighting capabilities. An LED bulb is transparent and allows all available light produced by the diode to pass through it, so to the naked eye, there’s no appearance of red, blue or other colors. Add electricity and the clear, low-profile light bar becomes alive with all kinds of bright, fun colors.
Some agencies like to promote the presence of red and blue lights on their vehicles, so the surrounding reflectors for each LED are colorized, giving the desired effect. Another option is adding colored, plastic dome pieces to the top of the light bar, and some LED light bars feature a daytime low-power setting that makes the color of the light bar visible without activating it in emergency mode.
Another tactical advantage : The intensity of LED bulbs can be determined by varying the amount of electricity going through them. This is helpful at night scenes where safety and control have been established, but some warning is still necessary. Because strobes and incandescent bulbs are limited in their ability to do this, overly bright warning lights can play havoc with night vision. Being able to control the degree of brightness can be helpful.
Consider also that traditional strobe setups flash by nature, so they’re impractical as a lighting source on nighttime traffic stops. Because LEDs are solid-state, electricity can be channeled through them for an unlimited amount of time with little heat buildup. It’s possible then to use red and blue forward-facing lights in conjunction with take-downs as a consistent, steady light source.
Color, Color Everywhere
My last patrol vehicle had a combination of strobe lights and LEDs. The overhead light bar consisted of strobe and incandescent bulbs. The main sections comprised a large strobe bulb, a reflector and a colored lens over it. This posed several problems. First, because the light produced by the strobe was white and multi-directional, there had to be a way to channel the light. Hence, the mirrored reflector. Second, there had to be a way to change the white light to the desired color. Hence, the colored plastic lens. Unfortunately, each of these steps detracted from the power of the original strobe flash. Coupled with UV rays oxidizing the plastic colored lens, the end result was less than spectacular. In fact, during the day, the tiny LED lights on my front push bumper were much more noticeable than the entire light bar on top of the truck when activated.
The brightness of LED lights over other choices, especially in the daytime where blue light needs to be three times brighter than red to be perceived equally by the human eye, make it essential for traffic clearing and early warning. Moreover, in the space that one strobe light has been designated to be red, there could be multiple LED lights, each with a specific color and duty.
Why is this important? In a landmark study on patrol vehicle lighting by Lt. James D. Wells Jr. of the Florida Highway Patrol, extensive testing determined that light bar effectiveness can be increased by communicating the position and current action of your vehicle. Motorists’ perception of distance and motion can prove problematic. Simply put, it’s hard for people to tell if your car is moving or stopped when they approach you.
Wells points out numerous guides that motorists use to gauge distance from and reactions to other vehicles, including familiarity with the road and other objects, visual angle, the relative size of one object vs. another, elevation changes, clarity and perceived closing speed. Despite having excellent visibility and no physiological issues, drivers routinely crash into stopped or slow-moving vehicles because they have difficulty judging closing speed, especially at night. That’s why officers with all of their rear lights activated on the side of an arrow-straight road with no obstructions still get rear-ended.
Given a similar situation, it may make more sense to use emergency lighting to direct or condition motorists to use proper avoidance behavior, rather than just alert them to a presence. The Wells study recommended that the color and frequency of the light bar be changed depending on the condition of the patrol vehicle. Examples : The light bar could be a different color when the vehicle is moving than when it is stopped. Amber warning lights could be used across the entire light bar or in the rear window, etc.
The study also concluded that LED lighting was the most effective light choice to do this, and, practically speaking, the size advantage of LEDs allows them to be stacked horizontally to create multiple layers of light and color options. To do that with a strobe or incandescent configuration would be completely impractical and make the light bar a foot tall.
What Are You Waiting For?
The entire purpose of emergency lighting is to provide visual communication to the general public about our role, purpose and intent. For us as officers, effective emergency lighting helps us do our jobs safer, which should be at the forefront of any equipment choice for patrol vehicles. As we have learned, LED emergency lighting options are brighter, more reliable and extremely durable, and provide a fraction of the power draw of other choices. They can be easily hidden without detracting from performance, and their size allows for mounting virtually anywhere. Add in the ability to produce multiple color schemes and configurations from a single light bar, and the choice is as clear as the bulb housing the LED: They belong on your patrol vehicle.