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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.
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.
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.
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