Photo Dale Stockton
LEDs project most light forward. Photo JP Molnar
FEATURED IN TECHNOLOGY AND COMMUNICATIONS
As cops, we like bright lights that tell people to get out of our way. We don t like getting hit by a car when we re on a traffic stop or at a crash scene. At the very least, it destroys our office; at the most, it kills us or someone else.
The latter has caused a lot of debate about what constitutes the best emergency warning system. Remember the great television show Emergency! ? The show, which debuted in 1972, showcased the latest lightbar technology, the now legendary Federal Twinsonic Lightbar, on Squad 51. That lightbar changed the idea of overhead lighting on emergency vehicles. Since then, the solid lightbar concept has remained relatively the same, with the exception of advancements to the light sources, such as strobes and LEDs.
Several years ago, one of my squadmates got a new Ford Crown Vic for patrol that formerly functioned as a tradeshow vehicle for an emergency lighting manufacturer. We were working graveyard, and I remember the first time he showed up to a cover call with a multitude of LED lights blazing in every direction. The car could be seen from space, but was it really safer?
To find out, I researched some of the leading studies conducted on the effectiveness of emergency lighting. Although numerous studies have been conducted on the perception of light by motorists, one landmark study specifically addresses two routine problems in law enforcement: police vehicles and officers being struck on traffic stops and crash scenes, especially
at night. The study, released by Lieutenant James D. Wells Jr. in 2004 on behalf of the Florida Highway Patrol (FHP), concentrated on emergency lighting configurations.
The study covers much more than I can address here, but I m including a synopsis of what should be a mandatory read for anyone charged with buying their agency s emergency lighting. Doing so could save money, aggravation and, more importantly, an officer standing on the side of the road.
Wells FHP Emergency Lighting Study
According to FHP statistics, from 1996 2000 there were 1,793 incidents in which Florida motorists crashed into emergency vehicles. As a response, the FHP and Wells began a comprehensive study designed to reduce that number. The study was all encompassing, but I ll focus on Wells evaluation of three different then-prototype lighting systems from Code 3, Federal Signal Corporation and Whelen Engineering. The study s emphasis was placed on human reaction to various lighting configurations relative to perception and action behaviors.
As far back as the ancient times, man used light in the form of fire to guide travelers or to warn them of impending risk. A few thousand years later, we re still at it, bolting red and blue lights to the roof of our patrol vehicles to both identify and warn motorists of law enforcement s presence. As motor vehicles have become faster and emergency lighting sources brighter, the general trend has been to put the most and brightest amount of lighting on a patrol car to provide the earliest warning times.
What s missing is the critical component of lighting s goal. As Well s study points out, the most important purpose of emergency lighting is to deliver a specific message to drivers. But what message? Are you simply trying to announce your presence, tell them to get out of the way, warn them of an upcoming hazard or use lighting to create a traffic pattern?
Activating bright lights without considering your reasons may do more harm than good. For instance, those lights might actually decrease the driver s ability to see emergency responders who are on foot working a traffic accident or debris that is in the roadway.
A second consideration: Proper lighting can communicate 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 of 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 of your presence.
The Moth Effect
Should you leave your emergency lights on during a traffic stop? Proponents claim the emergency lighting attracts attention and warns motorists of your presence and any possible hazards. Detractors claim that because people naturally drive where they look, the lights will actually attract them, especially impaired drivers, like a moth to a light bulb. As a result, some agencies require officers to extinguish all rear-warning lights on a freeway traffic stop, while other agencies leave it to officer discretion.
According to Wells, no known studies substantiate the notion that activated emergency lights cause drivers to crash into stopped police cars. He points out, and I agree, that there are numerous things drivers look at while on the road, including road signs, billboards, store fronts, etc., and no one seems to regularly drive into those items. In fact, an analysis of rear-end collisions by the FHP and the Illinois State Police determined no evidence supports the moth effect.
Comparing the accident frequency of fully marked, slicktop and unmarked vehicles also showed no appreciable difference. Furthermore, an analysis of 100 crashes by the Ford Motor Company s Arizona Blue-Ribbon Panel that studied serious rear-end collisions involving the Crown Victoria determined that no collisions occurred solely because drivers were mesmerized by the emergency lights.
As for impaired drivers, my personal experience with hundreds of DUI arrests and crash investigations has taught me that impaired drivers do everything bad while behind the wheel. In reviewing experiences with my own police vehicle and other troopers vehicles being struck on traffic stops and crash scenes, few were caused solely by drunks driving at our lights.
Wells refers to some existing data that suggests drivers do make adjustments to driving behavior when approaching a parked car, regardless of whether or not the vehicle s emergency lights are activated. The study suggests there s no validity to the moth effect, so officers may want to reconsider before turning off all rear emergency lights on traffic stops.
Red, Blue or Something Different?
As children, we learn that the color red generally means danger. As we get older and begin driving, red traffic signs reinforce that idea. A red light or sign means stop, reminding us to be vigilant. This concept has been carried into emergency lighting red has been the warning color of choice for decades.
Recently, blue lights and white lights have been integrated into lightbars. As Wells points out, the human eye is more sensitive to blue than red at night. In the daytime, the roles are reversed; during the day, a blue light must shine twice as bright as a red light to be perceived as equal in intensity.
Example: The lightbar on my last patrol vehicle was a strobe unit with blue, red and white lenses. Because all the strobe bulbs were powered equally, the blue lenses were barely visible in direct sunlight, the red lenses were more noticeable, and the white lenses were the best. At night, blue light needs roughly 1/3 the power of a red light to be perceived as equally bright. This means an officer can have a less intense light without being less visible.
Another phenomenon Wells discusses is the Blue Advancing/Red Receding Effect. At night, the human eye perceives a blue light as moving towards it, while a red light seems to be moving away, even when both lights are mounted side-by-side and illuminated together in darkness. This effect explains why drivers misjudge red tail lights at night as being farther away than they really are.
To prove this, Wells cites a study by Dr. L. Tijerina of the Arizona-Ford Blue Ribbon Committee on Lighting and Conspicuity that evaluated eight different overhead lighting systems. It compared drivers responses to approaching illuminated all-blue, all-red and combination color lightbars at night. The study also looked at the influence of multiple overhead lights vs. a single beacon light. The results: Blue lights significantly outscored the red lights at night and caused the test subjects to use the highest level of desirable driving behavior.
Other considerations: Blue lighting is more unusual to see on the roadway at night, so it stands out more as an anomaly. Also, regardless of the light source (i.e., halogen or strobe), placing a colored filter over a light reduces intensity, similar to placing a lampshade over a light bulb. The more translucent the shade, the greater the amount of usable light. The same thing happens on a halogen or strobe lightbar, and it s why white strobes are much more visible than red or blue ones.
Also, because amber isn t as dark as red or blue, it s much more visible when activated. Wells points out that this effect isn t true for LEDs because there are no filters involved. In such a case, red and blue colors can be as bright, or brighter, than amber.
How Bright & How Fast?
It s common sense that an aircraft landing light can be seen farther away than an AAA-flashlight. This is affected, of course, by the amount of ambient light around the source, but field experience teaches officers that even the crappiest overhead light is more visible at night than during the day.
According to Wells, the frequency of the illumination is more important. Although faster flash rates attract more attention, there are limits to what the human eye can perceive. Some halogen lights can be perceived
as brighter than strobes because, although not as bright, each individual flash is longer, allowing the human eye to register it.
In fact, sometimes steady lighting sources are better for communicating a vehicle s location than flashing sources. The brain can establish a consistent pattern and register an object s presence because the lights are consistent. Wells outlines a 2001 FHP comparison study of the use of steady flares and flashing lights to indicate lane closures. The steady flares were clearly superior in defining a course of action for drivers.
Importantly, the lighting configuration on any police vehicle should be positioned to produce long-range warnings that don t interfere with up-close vision. In other words, as drivers approach the vehicle, their line of sight should remain below the most intense warning lamps to see what s ahead. It doesn t mean you can t mount additional warning lights in rear windows, trunks, rear tail lights, etc. But because these lights will be closer to eye level when motorists approach, they should be lower in intensity to prevent excessive glare and night-vision problems.
The Wells study also looked at the effect of emergency lighting on night vision and determined that although the control group complained of night blindness, they actually had no problems identifying surrounding objects. Blue lighting was the least offensive.
Still, any officer who s been around illuminated lights at night especially LEDs knows they can be too-bright. Although there are advantages to warning motorists by using forward- and rear-facing LEDs, experience suggests that officers should use their discretion once on scene.
What s It All Mean?
This article merely skims over the information in the Wells study. It s very important for those interested to access the study online (see The FHP Study for URL).
In short, the study makes five recommendations. First, LEDs are the way to go, and lightbars should have both red and blue lights. Amber lights used for traffic arrows should be controlled separately and only activated when stopped or in a moving mode for escort purposes. Amber arrows are best for directing traffic. Most drivers see them, realize there s a hazard ahead and follow the arrow s directions.
Second, a solid color should be used when the vehicle is stopped, and a flashing pattern should be used when moving. Blue is better at night; red is better during the day. Amber should be used in conjunction with blue or red during a stop to address color-blindness issues.
Third, LEDs have limitations they project most light in a forward direction. There isn t much space for LED panels on the ends of lightbars, so the study recommends including a white halogen takedown light at each end of the lightbar to address intersection issues. (This recommendation includes lightbars with LED panels angled at 45-degrees away from the front and rear rows.)
Fourth, a flash rate of 90 flashes per minute with a 50-percent split between illuminated and non-illuminated bulbs seems ideal. A breakup pattern of multiple flashes should be incorporated every few cycles. Finally, a steady burn of all forward-facing LED lights can provide better illumination for take-down situations.
Many factors go into reducing collisions between parked patrol vehicles and the motoring public. Although we can t pave new roads or change the weather, using the valuable information in Wells study can help reduce collisions and save officers lives.
the fhp study