The only purpose of emergency vehicle warning lights is to be visible and understood immediately, whether during daylight, nighttime, in rain, or in traffic. Within this seemingly simple function lies a complex world of engineering, which encompasses LED optics and flash controllers, electrical load planning, and industry codes.
Therefore, for everyone who wants to determine, install, or service the equipment used on fleet vehicles, the question of how emergency vehicle warning lights operate must be answered accurately.
Currently, modern systems make use of LED light-heads controlled electronically, and this enables the establishment of flash patterns, synchronization, and brightness intensity. Optics shape the lighting to satisfy SAE standards, and the controller unites all lights, sirens, and status of the vehicle.
As indicated by the above discussion, there are multiple design compromises to be made, brightness should be regarded with respect to glare and power consumption, and drivers’ perception should always be compared to flash patterns.
From Rotating Beacons to LEDs
Originally, early warning lights operated with incandescent or halogen bulbs, which were attached to spinning reflectors. This technology produced the well-known rotating beam. Strobe lights came next and employed gas-discharge tubes for quick flashing. Both methods were effective, but had several limitations, such as extensive energy consumption and limited timing options.
Companies such as Whelen, founded in 1952 and headquartered in Chester, Connecticut, have seamlessly transitioned between the various generations of lights. In today’s market(s), LEDs dominate because of many engineering advantages.
First, they turn on and off almost instantly, allowing for the creation of complex flash patterns. Second, they use less electricity for the same output and because they have no filaments, and none of the moving parts found in traditional lighting systems, they will not fail due to vibration.
However, LED lighting systems do create an issue with excessive heat at the semiconductor junctions. Quality lighting equipment must have heat sinks designed to maintain acceptable junction temperatures and to ensure that containerized light tubes remain within normal temperature ranges even in the summer sun.
How Flash Patterns and Synchronization Work
In a modern system, each lighthead is driven by electronics that determine exactly when it turns on, for how long and at what intensity. A central controller, often combined with siren functions, coordinates the entire vehicle so that every light follows the same timing.
Synchronization matters more than it may seem. Lights that flash in a coordinated pattern read as a single, organized signal, while unsynchronized lights can appear chaotic. Many systems also allow alternating or phased patterns, where lights on opposite sides of the vehicle flash in turn to help convey the vehicle’s width and position.
Controllers can also adjust output based on conditions. Some reduce intensity at night to limit glare, change patterns when the vehicle is parked or trigger specific lights when doors open or the vehicle is placed in park.
Optics: Omnidirectional vs. Directional
Light emitted by a single LED is confined to a reasonably small angle, thus making use of optics to direct the light onto the desired shape of light output. The use of reflectors, lenses and Optics of total internal reflection achieves this process for any device, either making a light cone used to illuminate a broad area around the vehicle or a narrow beam projected forward.
Two SAE recommendations cover most of this in North America. SAE J845 defines the specifications for optical warning devices which may be used on emergency or service vehicles. SAE J595 dictates the limitations for directional flashing devices, which are typically directed in a more focused horizontal and vertical plane.
Each of the SAE specifications also refers to classes. Class 1 devices are generally assigned as primary warning lights for vehicles operating at higher speeds than the surrounding vehicles, such as fire and police vehicles.
Color, Modes and the Right-of-Way Problem
Every color means something, and its utilization is controlled. Each different type of vehicle shows certain colors depending on the region; therefore, red cannot be used in replacement of blue, amber or white. Fleet managers have to check regional regulations prior to designating a definite system.
Fire apparatus indicate the impact of context on design. For example, in the Buyer’s Guide for warning lights of the Fire Apparatus Manufacturers Association, there are two ways of operation. One of them is a way of asking for the right of way in the process of responding. The second is a way of blocking the right of way at the scene.
As the guide for Fire Apparatus manufacturers states, white light cannot be used for blocking mode. However, vehicles usually switch between modes automatically due to their status. Also, one of the features from the same guide shows that the optical warning system has to consume no more than 40 amps of electricity in blocking mode.
Power, Wiring and Electrical Load
Each warning system must fit into the electrical capacity of the vehicle in which it is placed. There is a competition for alternator output among warning lights, sirens, radios, data processors, and scene lighting in a vehicle that is idle for extended periods at a given location.
Design engineers and upfitters must determine the total current draw, select the proper wire sizes and fuses and install load management that will shut down equipment that is not needed any time the voltage drops to a preset level.
Although the improved efficiency of the LED makes it much easier to do these calculations, they are still necessary when additional devices or upgraded lightheads are added that could potentially overload the system.
Specifying a System That Works Together
As controllers, light systems, and sirens were created to communicate visually and aurally, multiple agencies opt to standardize around one manufacturer’s ecosystem for consistent sync, programming, and replacement components across a fleet.
For instance, in the case of Ultra Bright Lightz’s Whelen lineup, it includes lightbars, surface-mounted lights, grill lights, dash and visor lights, sirens, speakers, as well as control systems, which highlights the fact that this series of products is extremely comprehensive.
Equipment required for each vehicle depends on its intended function: whether it is a pursuit vehicle, fire truck, or utility truck requires different setups concerning coverage design, intensity, color combination, and control mode.
Before You Spec Your Next Upfit
First, verify your state’s color and use regulations, and the SAE standard applicable to your devices in relation to the intended applications of the vehicle. Once those are established, determining which lightheads, controller, and wiring to use will be an engineering issue, not a shot in the dark.