Source: https://www.extremetacticaldynamics.com/knowledge-base/state-statutes/pennsylvania
Timestamp: 2019-04-24 16:12:50+00:00

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The state of Pennsylvania requires emergency vehicles to use warning lights whenever they are on public roadways. The type and color of lights that can be used depends on the type of emergency vehicle you drive. Below is a general overview of what kind of emergency vehicle lights are acceptable, along with a link to the associated ordinance for easy reference.
What is an "Emergency Vehicle?"
Under Pennsylvania State Code §121.1,an emergency vehicle is defined as "any vehicle that is designed to provide emergency or special services." This includes police and fire department vehicles, ambulances, military vehicles, any vehicle designed to transport blood or hazardous materials or any vehicle that's driven by the state medical examiner or Coroner.
Furthermore, all rotating, flashing or oscillating lights must meet or exceed chromacity coordinate, Standard Color metric System J578D, or the Color Specification for Signal Lighting September 1978 or subsequent SAE standards. Refer to the statute text linked at the beginning of this section for more information.
Fire truck lighting systems need to meet the same standards as with police vehicles. Private vehicles used as fire vehicles must mount their lighting systems as described under 75 Pa.C.S. §4571(a). If two or more lights are used, they must each be of the same color. Fire trucks are not allowed to use different-colored lighting in Pennsylvania. For more information, refer to Pennsylvania statute §173(a)(5)(ii). Volunteer firefighters are also covered under these laws.
Pennsylvania statute §173.2 defines light standards for ambulances. Under this statute, ambulances must have at least one revolving or flashing strobe lights that are red, white or clear in color and at least two revolving or flashing lights that are blue, white or clear in color. Ambulances may also use light bars with these colors, but the light bar that's chosen cannot have more than two emergency lights.
§173.4 requires that all wiring used in the lighting system is SAE-rated and of a large enough gauge to be able to handle the electrical load put out by the system. The ground wiring must also be of equal gauge.
Furthermore,all ambulances need to use an activation indicator. The indicator must activate automatically whenever the vehicle's lighting system is engaged. Those who violate this law can be penalized under §173.6. Penalties may include sanctions imposed according to 75 Pa.C.S. §6502(b).
Construction truck lighting is covered under §173(a)(5)(ii),same as fire trucks. Unlike fire trucks, however, construction vehicles must use amber or yellow lighting, and any light bars installed will need to be amber or yellow in color. Furthermore, like ambulances, construction vehicles will need a light activation indicator that automatically turns on when the lighting system is engaged.

References: §121
 §4571
 §173
 §173

§173
 §173
 §6502
 §173