Do Emergency Vehicles have too many Warning Lights?
The use of LED-based lighting, which has become the standard for several reasons: Light-emitting diodes (LEDs) are small; the light is emitted via solid-state electro-luminescence; and they are powerful, efficient and long-lasting (as they have no filaments to burn out), and can be easily seen, even at great distances and in sunlight.
Let’s now turn to some of the studies of various forms of lighting.
A study at Loughborough University in the United Kingdom showed that strobe lighting conveyed a greater sense of urgency to drivers. The study also concluded that factors such as flash pattern were important, with forward-facing, simultaneously flashing lights attracting attention far quicker than alternately flashing versions—although this lighting set-up did increase glare. Not surprisingly, the higher the intensity of the light—and the more light sources (heads, beacons, etc.)—the faster attention was gained.
But what about color? The perception of color is controlled by the cones and rods of the eye. Red and blue lights are generally associated with fire and EMS (as well as police) and, naturally, many ask the question, which color is more effective? Red lights are good in the day because, at a distance, it’s difficult to see blue lights; and other data suggests that blue lights are more effective at night. However, some new studies claim that blue (especially LED versions) are the most effective. Period.
The study “Effects of Warning Lamp Color and Intensity on Driver Vision” by the University of Michigan/SAE International/USFA advises the following:
- Consider different intensity levels for day and night.
- Make more overall use of blue lights for use during both day and night for ALL emergency vehicles.
- Consider signals to distinguish stopped-in-traffic-path (red only) from stopped-out-of-path (blue only).
In a 2004 Florida Highway Patrol Study, the worst lights for signaling relative motion (is the patrol car moving or not?) were lights that alternated flashes from side to side. Also, the study indicated that when it comes to color, red LEDs are more visible in daylight than either blue LEDs or blue halogen lights. This is a combined effect of the red LEDs having more light output than blue, and the red light being more readily detectable in bright environments.
So with the advent of LEDs, blue has become a much more intense and visible color, appearing to be the best color to use at night because it is more conspicuous in the dark environment; it gives a truer perception of the vehicle’s motion than red, it stands out against the predominately red background provided by other vehicles, and we can use less intensity with the same perceived brightness, helping to reduce the likelihood of night blindness.
Speaking of … one factor not often addressed is the effect of flash rate on night blindness. Currently most lights flash with a 50% duty cycle (half the time on, half the time off). When it comes to the inner workings of the eye, what we see is actually somewhat delayed because, just like cameras, if we have a high enough flash rate, the eyes stay adjusted to the brighter lights and are not “blinded” by them.
In the Florida study, the best configuration for moving apparatus involved the light bar quickly and randomly flashing all the modules, red and blue, whether day or night. This gives them many flashes in red, blue and white, signifying (and perceived as) movement of the vehicle. When stopped, the entire light bar flashes as one complete unit at 90 flashes per minute in the color chosen according to the ambient light (red during the day, blue at night). So, when moving, it’s a multi-flash “dancing” pattern. When stopped, it’s a solid, large, light-synced, slower flashing pattern. Also, the lights will not flash in the rear window when the vehicle is moving unless specifically activated by the operator, possibly when accompanying a disabled vehicle from the roadway or to assist with an oversized vehicle escort.
So can there be too many lights? My conclusion is that it is all about how they are installed, positioned and used. So certainly, there CAN be too much lighting. For example, in January, a Metro Nashville officer was struck when motorists claimed they were blinded by all the warning lights and the positioning of emergency vehicles. “It was clear to all the other drivers that there was a collision; there were at least two police cars, an ambulance and a fire truck also tending to that first accident,” said one witness. But as a driver, the citizen said that was just the problem. “Once I passed the accident, the lights literally blinded me and even though I slowed down and was in the farthest lane over, I couldn’t see what was going on,” he said. At least two eyewitnesses reported that several emergency lights and police high-beam headlights were shining right into oncoming traffic, giving a blinding effect to drivers headed toward the officer. Another person stated that they hoped that drivers will learn from this to slow down and pay close attention to what’s ahead in an emergency situation. But, he also hopes that police (and fire, EMS, etc.) will remember where to shine their lights and where not to, especially in the dark.
Interesting, huh? All that for flashing lights. When you think about it, warning lights may actually be more “heroic” than we ever realized, as we have no idea how many accidents they have prevented.
Nozzlehead Note: My thanks to the Florida Highway Patrol as well as www.ResponderSafety.com; the IAFC Safety, Health and Survival Section; the IAFF; the USFA; Whelen Engineering; and Ken Menke III of PowerArc Warning Lights, sponsor of SAEJ2498, the national warning light standard for emergency vehicles, for providing information for this article.