Emergency vehicle lights and siren [duplicate]

Police cars or ambulances have lights on their roof, which are on when the sirens are on. What are these lights called? Is it something like signal lights or alarm lights?

I am looking for an official term/word.

Example sentence:

……………… create an interesting atmosphere at night.

The official term is lightbar/light bar

(noun) A bar mounted on the roof of a vehicle, such as a police car, with rotating beacons or other lights to provide a visual warning.

It is also labeled as such on the Merriam-Webster Visual Dictionary Online.

(Source: http://www.visualdictionaryonline.com/society/safety/crime-prevention/police-car.php)

A generic term for these lights seems to just be "Emergency vehicle lights." I have looked for a more specialised word, but even websites that sell these lights refer to them as such.

I guess you are looking for the word "beacon lights".

An excerpt from Wikipedia

Vehicular beacons are rotating or flashing lights affixed to the top of a vehicle to attract the attention of surrounding vehicles and pedestrians. Emergency vehicles such as fire engines, ambulances, police cars, tow trucks, construction vehicles, and snow-removal vehicles carry beacon lights

Here is a picture of such a light (Source: http://www.thehindubusinessline.com)