Why do emergency vehicles drive with blue lights?

Nee-naw! Nee-naw! An ambulance blazes through the junction. Nee-naw! Nee-naw! My gaze follows the vehicle’s light. The rotating beacons shoot beams of light in all directions so that they can be seen from any angle. Makes sense. The thing that gives me pause, however, is the colour. After all, the colour pulsating from the roof is blue, not the warning colour red.

Why is that?

You practically never see blue in traffic otherwise. Traffic lights are red, amber and green, while cars typically have white and red lights. With this in mind, you could argue that this makes the colour blue stand out. That’s one reason, but not the original one. In fact, warfare was at the forefront of decision makers’ minds when the colour was chosen.

In view of the Second World War, the German Reich introduced a new air protection law, which set out measures such as the implementation of blackouts. This was supposed to make it more difficult for enemy fliers [to navigate by night] (https://www.geo.de/wissen/18549-rtkl-endlich-verstehen-darum-waehlte-man-fuer-blaulicht-die-farbe-blau-und-nicht-rot). Since the atmosphere scatters blue light more than other colours, blue can’t be recognised above a height of 500 metres. Fire trucks, which had always been equipped with red lights on account of their association with danger, had to be refitted. Police cars, however, had hardly ever driven with special lights up until that point.

After the Second World War, many fire fighters reverted to red lights, probably in a nod to tradition. Blue-light advocates, however, argued that the use of red lights might cause confusion at traffic lights or level crossings. They prevailed. In 1951, blue lights were officially mandated in road traffic licensing regulations. From then on, the trend spread to emergency service vehicles all over Europe.

Spain has been one of the few countries to break with this European convention and equip its ambulances and fire engines with amber lights. This is down to a law stating that only the police are allowed to drive with blue lights. In the rest of the world, however, red lights are often still in use – the USA, Canada and Japan being prime examples.