What is the purpose of Runway End Identifier Lights (REIL)?

Runway End Identifier Lights (REIL) serve the essential purpose of enhancing visibility by marking the ends of runways, particularly at airports where the runway might be difficult to see due to existing lighting conditions or weather issues. They consist of a pair of synchronized, flashing lights located at the runway ends, typically one on each side. These lights are particularly beneficial during low light conditions, such as twilight or nighttime, to ensure that pilots can adequately identify the runway's termination point.

By clearly indicating the limits of the runway, REIL aids in ensuring safe landings and takeoffs, providing pilots with critical information for distance judgments and aiding in runway alignment. This focus on visibility aligns perfectly with the role that REIL plays, as opposed to other functions like marking the runway centerline or providing navigation during taxiing.