Active visual warnings

Main article: Emergency vehicle lighting

An ambulance in Denmark with roof-integrated LED lights, plus side-view mirror, grill and front fend-off lights, and fog lamps wig-wags
The active visual warnings are usually in the form of flashing lights. These flash in order to attract the attention of other road users as the ambulance approaches, or to provide warning to motorists approaching a stopped ambulance in a dangerous position on the road. Common colours for ambulance warning beacons are blue, red, amber, and white (clear). However the colours may vary by country and sometimes by operator.
Emergency lights may be housed in special fittings, such as in a lightbar, or may be hidden in a host light (such as a headlamp) by drilling a hole in the host light's reflector and inserting the emergency light. These hidden lights may not be apparent until they are activated. Additionally, some of the standard lights fitted to an ambulance (e.g. headlamps, tail lamps) may be programed to flash. Flashing headlights (typically the high beams, flashed alternately) are known as a wig-wag.
There are several technologies in use to achieve the flashing effect. These incluse flashing a light bulb or LED, and strobe lights, which are usually brighter than incandescent lights. Each of these can be programed to flash singly or in groups, and can be programmed to flash in patterns (such as a left -> right pattern for use when the ambulance is parked on the left hand side of the road, indicating to other road users that they should move to the right (away from the ambulance). Incandescent and LED lights may also be programed to burn steadily, without flashing.
In order to increase safety, it is best practice to have 360° coverage with the active warnings, improving the chance of the vehicle being seen from all sides. In some countries, such as the United States, this may be mandatory.
See also Emergency vehicle equipment.