Why do beacons on Police cars flash Blue and Red lights?
There is practical advantage of using two colors for high intensity lights on police car beacons. Blue is easier to see during daytime and red more clearly discerned at night. Blue also is chosen for its long association with police in US (e.g: blue lights in front of police stations, blue uniforms in many states) and because of its high daylight visibility. Red has long been a symbol of warning and danger and a signal to stop. No other emergency service uses blue in its beacon. Firefighters and ambulances use red. Construction and emergency transport vehicles (towing etc.) use yellow or amber. Only police beacons are two-colored. Some states/cities have experimented with all-Red beacons (e.g NY capital city Albany, where I am on a visit currently), while some cities have tried with all-Blue (e.g our Chicago police) beacons. However, the most common is Right-Blue, Left-Red beacon.
