Green lights on vehicles have specific emergency, official, or service-related purposes, depending on local laws. They may be used by volunteer firefighters or EMS personnel responding to emergencies, while green lights at emergency scenes can identify command vehicles and help responders locate incident commanders quickly.

In some jurisdictions, government, security, or specialized agencies may also use green lighting. Certain highway maintenance and repair vehicles may be authorized to display green lights, while private security vehicles may use them in limited circumstances. These rules vary significantly between states and countries.

For ordinary civilian vehicles, displaying green lights is generally prohibited unless specifically authorized. For example, some jurisdictions restrict or prohibit flashing green lights on civilian vehicles. Green lights may sometimes serve as courtesy or identification lights, but they do not necessarily give the vehicle legal emergency privileges or the right of way.

If you see green lights on a vehicle, the driver may be a volunteer first responder, government or security official, or authorized service worker. Unauthorized use can lead to traffic stops, fines, or other penalties. Because regulations differ by location, drivers should always check their local vehicle and emergency-lighting laws before using green lights.