Controlling the Scene Jim Stopa
In October, as the days grow shorter and it gets darker, first responders are increasingly called to emergency scenes with little or no daylight.
This time of year, many of us are thinking about how to increase safety at a nighttime emergency scene and, naturally, “having the best lights” is often at the top of the list. So, what makes one light better than another? Contrary to what you might think, it is not more lumens.
While a lumen is a simple number, easy to reference in marketing materials and manufacturers’ quote-writing programs, lumens don’t tell us the whole story about a light’s performance. One of the best ways I’ve heard someone put lumens into perspective is through the fire hose analogy. Let’s say you have X amount of pounds per square inch (psi) in a water tank pumping system, and you need to spray it through the hose nozzle. In this example, the tank and pump pressure represent lumens, and the nozzle represents a light’s optic. The nozzle spreads the water in a direction through a focused stream or by fanning out, just like the optic focuses a light in a specific direction. Is it narrow? Is it wide? Is it symmetrical or asymmetrical? These are crucial details, which have little or no relationship to psi. Where the water is going and how far it can travel (optics) are just as important as having water pressure (lumens) in the first place (Figure 1).
Figure 1: The hose’s nozzle focuses the water spray, just like a light’s optics focuses the beam of light. (Images courtesy of Whelen Engineering.)
A fitting example would be Whelen Engineering’s 2-Degree, 8-Degree, and Wide-Flood PAR46 illumination models. All serve different purposes but have the same number of lumens. If the 2-Degree PAR46 had one more diode, it would have a higher lumen rating; however, it would not be the most effective choice if you were trying to flood an area with light.
Here is another example to show how lumens don’t correlate with a light’s performance. A typical 10,000-lumen scene light mounted properly on a fire or EMS apparatus optically projects light downward, illuminating a wide area of the ground. The same 10,000-lumen scene light mounted upside down optically projects light upward with little or no light illuminating the ground. So, the same 10,000-lumen number has two very different illumination outcomes because of the different optic design (Figure 2).
Figure 2: A 10,000-lumen number has two very different illumination outcomes depending on the optic design.
Michael Piscitelli, CEO of Sapphire Technical Solutions and vice chairman of the SAE Emergency Warning Lights and Devices Committee, compares the misinformation about lumens in the emergency scene lighting industry with what happened in the flashlight industry.