Marked EMS vehicles are frequently struck in the rear at crash sites or intersections by civilian vehicles. As previously discussed in this column (see related links below for more), sirens aren't very effective. But because eyes are our primary method of gathering information, effective lighting can be. Fortunately, a solution exists through the application of a reliable technology that begins with exciting a lot of electrons in a very small space, which results in 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.
The Atom Dance
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's comprised of two types of negatively and positively charged materials. When no current is applied, each side essentially holds its own. But apply current, and the negatively charged atoms essentially cross over the semiconductor and "invade" the positive side. In doing so, the negatively charged atom has to "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 of your TV remote). In others, the gap is larger and the frequency wavelength enters the visible spectrum. Add more electricity, get more photons, and voila: You get 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 aren't reliant on reflectors like incandescent or strobe bulbs. Diodes are one of the simplest types of semiconductors and are very efficient because all of the electricity applied goes toward the production of light. Diodes also very durable and vibration-resistant because there's no filament or moving parts to worry about. So how does this compare to incandescent and strobe bulbs?
Be Cool with LEDs
Incandescent bulbs have a filament in them that has to be heated to produce enough temperature to create visible light. In fact, a typical light bulb filament runs at about 4,000 degrees, which is the heat necessary to produce enough photon release to generate enough visible light. 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. As an example, a nine-watt LED bulb can perform as effectively as a 60-watt bulb and produce a whiter light. It also does this with much less heat because there's no filament to heat up. In fact, the temperature is so much lower that plastic can be used for the bulb construction.
Another 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. By contrast, traditional strobe and incandescent setups require external reflectors to direct the light. This means that the application in EMS vehicles becomes limited, and performance suffers as reflector size decreases. Yes, intensity can be increased in the form of more powerful bulbs (read: power suckers), 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 be pretty much mounted anywhere. 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. The flexibility of LED choices is so large that there really is no reason to not integrate them into your EMS 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.
The intensity of LED bulbs can be selected by varying the amount of electricity going through them. This is helpful at nighttime scenes where safety and control has 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 wreak havoc on night vision. Consider also that traditional strobe setups flash by nature, so they're impractical as a lighting source on nighttime traffic crashes or other incidents. Because LEDs are solid-state, they have the capability of channeling electricity for an unlimited amount of time with little heat buildup.
Let's compare a traditional strobe or rotator bar (still in use many places) with an LED light bar. The overhead light bar consists of strobe and incandescent bulbs. The main sections are comprised of a large strobe bulb, a reflector and a colored lens over it. This poses several problems. First, since the light produced by the strobe is white and multi-directional, there first has to be a way to channel it; 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 detracts from the power of the original strobe flash. Coupled with UV rays oxidizing the plastic colored lens, the end result is less than spectacular. In fact, the tiny LED lights on a front bumper can be much more noticeable than the entire strobe light bar on top of a rescue rig when activated. The brightness of LED lights over other choices, especially in daytime, when blue light needs to be three times brighter than red to be equally perceived by the human eye, makes 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.
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 EMS personnel, effective emergency lighting helps us do our jobs safer, and safety should be at the forefront of any equipment choice for rescue vehicles. As we've learned, LED emergency lighting options are brighter and more reliable, extremely durable and draw a fraction of the power of other choices. 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 EMS vehicle.