Visual warning lights fitted to a vehicle
Emergency vehicle lighting, also known as simply emergency lighting or emergency lights, is a type of vehicle lighting used to visually announce a vehicle's presence to other road users. A sub-type of emergency vehicle equipment, emergency vehicle lighting is generally used by emergency vehicles and other authorized vehicles in a variety of colors.
Emergency vehicle lighting refers to any of several visual warning devices, which may be known as lightbars or beacons, fitted to a vehicle and used when the driver wishes to convey to other road users the urgency of their journey, to provide additional warning of a hazard when stationary, or in the case of law enforcement as a means of signalling another motorist that a traffic stop is being initiated. These lights may be dedicated emergency lights, such as a beacon or a lightbar, or modified stock lighting, such as a wig-wag or hideaway light, and are additional to any standard lighting on the car such as hazard lights. They are often used along with a siren system to increase their effectiveness and provide audible warnings alongside the visual warnings produced by the lights.
In many jurisdictions, the use of emergency lights may afford the user specific legal powers, and may place requirements on other road users to behave differently, such as compelling them to pull to the side of the road and yield right-of-way in traffic so the vehicle may proceed through unimpeded. Laws regarding and restricting the use of these lights vary widely among jurisdictions, and in some areas non-emergency vehicles such as school buses, and semi-emergency vehicles such as tow trucks, may be permitted to use similar lights.
History.
Early emergency lights were often red lights mounted to the front or roof of a vehicle.
The use of the blue emergency light originates in Germany during World War II. As a result of the "Verdunkelung", a black-out measure for aerial defense from 1935, cobalt blue was regulated to replace the red color used until 1938 in German emergency vehicle lights. Due to the scattering properties of the blue color, it is only visible to lower altitudes and is therefore less easily spotted by enemy airplanes.
Purpose.
Emergency vehicle lighting is generally used to clear the right of way for emergency vehicles, or to warn approaching motorists of potential hazards, such as a vehicle that is stopped or moving slower than the rate of traffic, or a car that has been pulled over. It may also be used to provide specific directions to motorists, such as a command to pull over. Some vehicles incorporate a small arrow board to direct traffic.
The use of emergency beacons is restricted by law in many jurisdictions only for responding to an emergency, initiating a traffic stop, bona fide training exercises, or when a specific hazard exists in the road. Most private security agencies have special permits that allow them to use beacons in specific areas. It has yet to be determined whether autonomous vehicles will be required to carry lights, or what colors or patterns they might exhibit to warn off aggressive human drivers.
Optical types.
The optical and mechanical characteristics of the lights used can have a significant effect on the look of the vehicle and how readily it gains attention in emergencies.
Steady burning.
The simplest form of lighting is a steadily burning lamp. These may be white lights used on scene to enable emergency workers to see what they are doing, or they may be colored lights that advertise the emergency vehicle's presence. In the latter case, steadily burning lights are often used alongside rotating or flashing lights rather than on their own, though historically some emergency vehicles only displayed steadily burning lights. For example, California Vehicle Code Section 25252 states: "Every authorized emergency vehicle shall be equipped with at least one steady burning red warning lamp visible from at least 1,000 feet to the front of the vehicle."
Rotating light.
These revolving lights may contain a single, stationary bulb around which a curved mirror is spun (or which is attached to a spinning mirror), or a lamp with a Fresnel lens. This creates rotating beams of light, appearing to flash when viewed. Larger rotating lights may contain modular or sealed-beam lamps which rotate as an assembly (commonly two or four bulbs, but possibly one or three).
To protect the workings of the beacon, a plastic dome often covers the assembly. These domes usually come in solid colors, but in some cases the front and back halves of the dome are different colors. Other beacons use a clear dome with colored lenses on each lamp; in the latter case, these rotating beacons are sometimes referred to colloquially as ‘gumball machines’ or sometimes ‘cherry tops’ in the case of red lights.
Rotating lights often use a quartz-halogen or conventional incandescent bulb, though some rotating beacons are now made with LEDs rather than bulbs.
Rotating lights may be used in lightbars as well as in single beacons. In a modern enclosed lightbar, generally ‘V’- or diamond-shaped mirrors are provided between the lamps to give the effect of multiple flashing lights.
Strobe lights.
Some emergency lighting is based on strobe lights similar to those used in flash photography. These xenon flash lamps put out a very brief but very bright flash by discharging a large current through a gas which ionizes it. The light produced has a somewhat bluish emission spectrum, which makes red lightbars glow a fuchsia-pink color when lit.
Strobe lighting did provide intense light which could improve visibility, but the short duration of the individual flash made it necessary to design the electronics to issue multiple consecutive flashes before alternating with the other associated lens pair. This purportedly allowed time for the human eye and mind to key in and observe the source of the light. Since the changeover to LED lighting units, which could easily allow for longer duration illumination time, they have instead chosen to mimic what is actually a shortcoming of the strobe light, and design the LED light head to illuminate with multiple short duration flashes. It has been noted that depending on the surrounding lighting conditions and other vehicle lighting, strobe only warning lighting did not allow for the same level of perception of distance from the source that traditional light bar and incandescent flashing lights would provide, especially on dark highways and similar locations.
LED lighting.
Light-emitting diodes are small, completely solid state, very power-efficient, long-lasting (as they have no filaments to burn out) and can be seen very easily even at great distances and in sunlight. LED emergency lights entered standard use around the 2000s and 2010s, replacing most rotating and strobe lights.
Whether as lightbars or single beacons, LED-based lights typically use a clear, colorless dome because the light color is an intrinsic property of the LEDs themselves. LED-based lightbars can be made very thin, reducing wind resistance by around 8-10 percent, or made very flat and used in novel applications, for example to flip up under a sun visor.
LED lights are often used in a mode similar to conventional strobe lights, however they can be programmed with a wider variety of flash patterns because of their ability to be switched directly by electronics, as opposed to discharging a capacitor through a gas-filled tube.
LED lights produce relatively little heat when in use. In colder inclement climates, this has resulted in LED emergency vehicle warning lights (as well as traffic lights) being obscured by the buildup of frost or snow, raising safety concerns. Solutions are being researched to provide a heat source, as necessary in certain weather conditions, to keep LED lights clear of snow and frost.
Modification of stock lighting.
The vehicle's stock lighting may also be modified to add flashing and strobe effects. This can be done by adding electronics to the existing lighting system (for instance, to create a wig-wag), or by drilling holes in the reflectors of stock lighting and inserting flashing lights in those holes.
Information matrix signs.
Some emergency vehicles use signs made up of a large number of light sources (usually LEDs), which can be programmed to display messages to other road users. This can be used to request other vehicles to pull over, indicate a special instruction, or just to display the name of the operating service (e.g. "Police").
Mounting types.
Emergency lighting may be fitted to several places on a vehicle, depending on the degree of conspicuity required. Beacons and lightbars are often mounted on the roof for high visibility, while other lights may be mounted on the body, in the grill, or in the interior of the vehicle.
Roof-mounted single beacon.
Since their introduction in 1948, rotating beacons have become widely accepted as a means of attracting attention to one's vehicle. Although the use of the single beacon in law enforcement has dropped since the introduction of light bars, they are still used by some police departments, because of their lower cost or due to tradition. One agency that continues to employ traditional red rotating beacons on its patrol cars is the Michigan State Police. Beacons are also occasionally used on construction equipment when a full-sized lightbar would be unnecessary or impractical to attach to the vehicle.
While many single beacons use rotating lamps or mirrors, others use strobe lights under a translucent dome to provide an omnidirectional flash. Some smaller and low-cost beacons of the latter type, however, are simply a blinking incandescent bulb. LEDs are also used to light some omnidirectional beacons.
The single beacon is also available with a magnetic mount for situations where permanent mounting is impractical. Examples of such situations would be detectives in unmarked vehicles, volunteer firefighters, or managers at freight yards who use an amber light for safety. These ‘mag-mount’ beacons are often round or teardrop-shaped, and are often referred to as ‘Kojak’ lights after the popular 1970s TV detective who used one.
Lightbar.
Originally, this referred to a simple metal bar on the roof of the vehicle upon which agencies would mount two rotating beacons, as well as other components such as sirens and stationary ‘lollipop’ lights. Soon the beacon manufacturers began producing off-the-shelf complete ‘lightbars’.
Later, the individual components of the lightbar were integrated into a single contiguous unit, with two elongated domes on either side of a siren enclosure. The extended domes allowed for more rotating beacons, additional mirrors, and fixed-beam lights toward the center to replace the ‘lollipops’.
Lightbars may now contain fixed, rotating, strobe, or LED-based lights in various configurations and offering programmable flash patterns. They may include a second, lower, tier of lamps, such as clear halogen ‘takedown’ lights towards the front to illuminate the vehicle being stopped, clear side-facing ‘alley’ spotlights, additional amber or red towards the rear for scene protection, or directional traffic advisory arrows. The modern trend of locating sirens on or near the front bumper of emergency vehicles has resulted in many lightbar models eliminating the siren housing in lieu of more lighting.
Some lightbar variations are specialized to meet certain desires of the agencies utilizing them, such as those using multiple rotating beacons in a ‘V’ pattern to provide additional illumination to the sides of the vehicle, and those designed to hug the roof of a vehicle to minimize air resistance or present a lower profile for ‘stealth’ purposes.
In Japan, many urban emergency vehicles will have lighting that can be mechanically raised when parked to provide greater visibility and safety for personnel working on the ground.
Body mounted.
Some types of light can be mounted on to the outside of the vehicle (usually a permanent install) and these can be used to provide directional lighting in key areas, such as in front for clearing traffic, or to the rear for scene protection. They can also form part of the main lighting arrangement for subtly marked or unmarked vehicles. In this application, the operating service may choose to use lights with clear lenses so as to minimize the possibility of the lights being noticed when not on.
Common places to mount such beacons include on or in the grill of the vehicle and on the front of the rear view mirrors, where they can gain maximum visibility. In the UK many emergency vehicles have lights on the side of the bonnet, which helps to warn oncoming traffic when pulling out of junctions. These lights are often strobe or LED types, as they have the lowest profile for purposes of attachment.
Interior mounted.
A variety of emergency