From take-off to landing, a jetliner’s external lights are vital to seeing and being seen. 
The Exterior Lights team in Getafe, Spain sets requirements for industry suppliers to design and manufacture such lighting – ensuring correct operation in all conditions, including very cold temperatures at high altitudes and high temperatures in hot climates, and the vibrations encountered during a typical flight. Another aspect is ensuring the right electrical bonding in case of a lightning strike. 
“Our main role is to gather data on state-of-the-art technologies and set out specific design requirements to instruct suppliers in designing lighting systems to meet operators’ needs,” said Amelia Martin, Head of Exterior Lights. 
Aircraft lights are divided into two broad categories: those used to help pilots see, and those that make the aircraft visible to others.
Like the headlights on a car, powerful forward-facing lights are switched on during darkness and in inclement weather to help flight crews discern the ground in front of them. Referred to as landing, taxi and take-off lights, these super-bright lamps are employed during taxiing, take-offs and landings. Other lights are used for visual ice detection on engines and wings, while additional ones illuminate areas on the aircraft with camera coverage. 
Lights that help make an aircraft visible to others trace their origins to maritime traditions: a red light on the port (left) side; a green light on the starboard (right) side. Complemented by flashing white and red lights in the wings, fuselage and tail, they all help to determinate an aircraft’s position and direction. 
Finally, aircraft have their vertical tailfin illuminated by a so-called logo light. More than just solidifying a carrier’s brand identity, such a large bright surface also makes the jetliner more visible – both in the air and on the ground. 
All told, there are a total of 23 external lights on a single-aisle A320 Family jetliner, and 41 on the widebody A350 XWB.

Seen head-on, this Airbus A320neo shows its port (left side) and starboard (right side) red and green position lights