Are Your Emergency Warning Lights Working For You?
The most important warning device on an emergency vehicle is its lighting system. That’s not by choice of the fire service, but rather due to the conditions of modern society. Today’s passenger vehicles are soundproofed to deaden outside noises, including sirens. Whatever residual sound does penetrate these cars is overshadowed by stereos, which are designed for the specific purpose of insulating the vehicle occupant from the irritation of traffic noise. Only the most powerful siren can now compete against the heavy insulation that is routinely installed in today’s cars.
In the interest of public safety, the fire service has tried increasing the decibel output of sirens to penetrate car interiors. Ironically, this has created a safety hazard to emergency personnel. Continuous exposure to high-decibel sirens can result in hearing damage. Sirens produce more than the 85 decibel (db) level, which is the Occupational Safety and Health Administration (OSHA) allowed maximum in a workplace. Some sirens can produce decibel readings as high as 130 db, which is the pain threshold.
Emergency lighting, by itself, is not always an adequate warning system. However, the effectiveness of its chief companion, the siren, is often downplayed simply because it’s in competition with many other outside noises. The siren is dependable as a warning device only when the emergency vehicle is in extremely close proximity to the motorists being warned. When the siren is coupled with a powerful air horn, fire apparatus have at least some chance to get the motorists’ attention.
Another “warning system” is vehicle color. Traditionalists who favor red as the color for fire apparatus argue that the public recognizes red, but will not necessarily associate yellow, lime green, or any other color with a fire truck. The contemporary yellow/lime green proponents respond that color association is a learned response, and that the public’s understanding can be changed.
By way of rebuttal, the traditional red truck advocates note that vehicle color perception depends on background colors, whether it is daytime or nighttime, and the public’s continuous exposure to other types of vehicles that are painted the same color as the city’s fire trucks.
Because there is no national color standard for the exclusive use of emergency vehicles, the debate on which color is most effective in warning the public is merely academic. Both sides have valid points. But, it is evident that we will never be able to agree on one single color as being the most dependable for identification/warning.
In tomorrow’s world, there may be a system such as Opticom* in every community. Or, someone might design a radio activated warning sound for use in all private cars, which would announce the approach of an emergency vehicle. But, in today’s world we have to work with market availability and what’s affordable.
Lighting is the most important warning device we have now because sirens and air horns cannot compete with soundproofing technology, and there is no consensus on the most effective vehicle color. Therefore, we must delve deeper into studying emergency vehicle lighting. Fortunately, the research that has been conducted thus far does provide important guidance on the best types and position of emergency lights.
EMERGENCY LIGHTING SYSTEMS
There are three categories of emergency lighting systems:
- placement on the vehicle.
Types of lights
In his report on strobe and rotating beacon lights, Dr. Timothy KeithLucas of the University of the South, in Sewanee, TN, discussed the advantages and disadvantages of strobe lights and rotating beacon lights. Here are the advantages of strobe lights:
* Opticom is an emergency vehicle preemption signal. It is a strobe light that is installed on the emergency vehicle and set at a controlled frequency. As the vehicle approaches an intersection, the light is read by a receptor that is mounted on the traffic light there. The strobe activates the traffic light to turn green so the oncoming emergency vehicle can proceed safely through the intersection. This system currently exists in only a few cities because it is very expensive to purchase and install.
Photo by Glann Usdin
- Strobes are far superior to rotating beacons during bright daylight conditions because of their higher peak intensity.
- It is preferable to use strobes during periods of poor visibility due to fog, rain, or smoke. Atmospheric particles reflect light, thereby reducing the peak intensity of a light source before the light signal reaches the viewer’s eye. Since beacons have lower light intensity than strobes, the viewer will perceive less light coming from them than from strobe lights.
- Light from a beacon drops off rapidly when the viewer is two or more degrees above or below the center of the beam. There is little “dropping effect” from a strobe.
- Contrary to popular belief, the strobe is less likely than the beacon light to be blinding to the eye, since blinding is caused by light quantity rather than its peak intensity.
- Beacons appear brighter (but more blinding) at night and over short distances.
- The viewer has depth perception difficulty (judging distance of light source from the viewer) at night with strobes, unless the strobe is reflecting off of a nearby object. Depth perception is a product of binocular vision. The viewer needs points at which his view can be fixed. Since strobe flashes are so brief, there aren’t enough visual clues for the eye to fix on. Viewers have better depth perception viewing a beacon at short distances at night because of the residual light between flashes.
- Used alone, rotating beacons are easier to visually locate than strobes.
Some advantages of the rotating beacon are:
Dr. Keith-Lucas offered an important recommendation in his report: “. . . strobes should not be used at night as the sole source of light from an emergency vehicle.” As a corollary to that point, a United States Department of Transportation study found that under daylight conditions, the strobe light did not compare favorably to sealed beamed lights because of their brief peakout period; “distance thresholds” improved with slower flashing lights.
At this point, we can conclude that strobes are superior to beacons in drawing attention, they can be placed high on a vehicle, such as the roof top, and they remain effective because there is little “drop off” as the viewer’s eye gets higher or lower than the light source. They do a better job than beacons of “penetrating” smoke, rain, or fog because they have more intensity than beacons.
Beacons are superior at close range because they offer a reference point for the viewer to gauge distance. That becomes a critical factor as the emergency vehicle gets close to the motorist.
Color of emergency lights
Previous studies of emergency light colors and their apparent influence on motorists indicate that a red strobe light is more visible and does the best job of reducing traffic congestion in bright sunlight. In darkness, the blue color strobe light works best.
Interestingly, red can be distinguished at a greater distance than any other color, but people tend to perceive it as being further away than it really is. People also tend to react slower to red at night than during daylight. In both daylight and darkness, a combination of blue and red lights is the most effective in moving traffic out of the path of emergency vehicles. Amber lights consistently evoke greater speed reduction.
Dr. Keith-Lucas has noted that adding blue or red filters to a light reduces the peak intensity in total light output by as much as 25%. The greatest loss occurs by putting a red filter on a strobe, and a blue filter on a beacon. It would therefore seem that you minimize light loss by using an unfiltered or redfiltered beacon light and a blue filter on strobe lights.
If you first ask “What work do I want the lights to do?,” color choices become easier. The objective of having lights on the rear of the vehicle is to initially slow traffic down. Amber lights do that best. Lights on the front of the vehicle must make motorists respond by moving out of the emergency vehicle’s lane.
Since the superiority of blue versus red lights depends on whether it is daylight or night, a combination of both is best. Avoid using a red filter on a strobe light and a blue filter on a beacon light.
Placement of warning lights
Fortunately, the advantages of each type and color light permits some common sense placement of the lights. When we apply the information discussed above to the “time-flow” chart on page 45, which simulates the motorists’ view of an oncoming emergency vehicle, the objectives of the lighting system change.
Stage I: The emergency vehicle is too distant to be clearly visible to the motorist. The lighting system objective is to attract attention. A clear (unfiltered) or blue strobe is best. To enhance the light source visibility, this lighting fixture should be roof mounted so that it is not blocked by other vehicles on the road. The strobe has superior penetration capabilities to cut through visual obscurities such as fog, smoke, or rain.
Stage II: The emergency vehicle and motorist are sufficiently close so that a prudent driver will begin to think about how he or other traffic will be yielding to the emergency vehicle. The speed, direction of travel, and proximity of the emergency vehicle must be perceptible to the motorist. If the information signals to the motorist are clear, the chances improve that the motorist will make prudent driving decisions.
In order to identify the location and travel direction of the emergency vehicle, binocular vision of the emergency lights on a continuous basis is imperative. The motorist can’t wait for a light “flash” to see the vehicle. The light must be visible when the motorist looks for it. Strobes do not meet that need for this observation stage, but beacons, or a combination of beacons and fixed beamed lights, do.
Because depth perception and the ability to locate the lights at any time are so important during this stage, the slower flashing light with significant residual light between flashes should be mounted at a level easily visible to the motorist. Side-marker and grillmounted emergency lights should be of this type. Unfiltered and red or red/blue combination lights produce optimum results for this type light.
Stage III: The motorist and emergency vehicle are within a block of each other. The motorist must now execute his yield. He now hears the siren and can identify the type of emergency vehicle that is approaching. His attention is drawn to an eye-level view of the vehicle. In order for the motorist to safely yield, he must be continuously aware of the emergency vehicle’s location.
If the motorist first sees an approaching emergency vehicle through his rear view mirror, then this is the only “stage” during which he became aware that an emergency vehicle was approaching. He did not have the benefit of Stage I and Stage II preparation. He must react almost spontaneously and in a manner that is predictable to the emergency vehicle driver.
A motorist in this situation can give only momentary sporadic glances in his rear view mirror. Specific emergency vehicle lights should be mounted on the emergency vehicle at a height that will clearly and reliably inform that motorist of the emergency vehicle’s position and speed. Grillmounted beacon or beam lights with ample residual flash are best suited for this role.
Remember, the function of a siren and air horn is to catch the attention of the motorist who did not see the emergency lights. When the emergency vehicle is in close proximity to an unaware motorist, a siren or air horn can and does cause unpredictable motorist response. The motorist reacts from fear and shock, rather than reasoned judgment.
And then there are the deaf motorists, or those who cannot hear outside sounds due to radio music or loud conversation in the vehicle. The siren simply will not compensate for ineffective emergency lighting. It is a last resort emergency signal. Many times, sirens are used to express the emergency vehicle driver’s frustration and irritation with a motorist who is unwilling to yield.
The environmental conditions in which emergency vehicles operate are continually changing. In the past, everyone was expected to unconditionally yield to fire apparatus because there was little traffic congestion, no radios or air conditioning to block out siren noise, and an instant recognition of and a community respect for the municipality’s fire truck.
Today, emergency vehicles are perceived as another roadway nuisance, probably en route to a false alarm or a coffee break. They are marginally capable of being noticed among other objects competing for the motorist’s attention.
In order to attract the driver’s attention, emergency lighting must be continuously evaluated and upgraded. A single red sealed beam light, once effective, is a ridiculous form of emergency lighting today. Similarly, the practice of using beacons, strobes, or red filtered lights independently of each other is outdated.
Hopefully, technology will solve the emergency responders’ dilemma sometime in the near future. Until then, the refinement of emergency vehicle lights, and your careful selection and placement of them, will keep your emergency warning lights working for you.