AIM Text
- Runway edge lights are used to outline the edges of runways during periods of darkness or restricted visibility conditions. These light systems are classified according to the intensity or brightness they are capable of producing: they are the High Intensity Runway Lights (HIRL), Medium Intensity Runway Lights (MIRL), and the Low Intensity Runway Lights (LIRL). The HIRL and MIRL systems have variable intensity controls, whereas the LIRLs normally have one intensity setting.
- The runway edge lights are white, except on instrument runways yellow replaces white on the last 2,000 feet or half the runway length, whichever is less, to form a caution zone for landings.
- The lights marking the ends of the runway emit red light toward the runway to indicate the end of runway to a departing aircraft and emit green outward from the runway end to indicate the threshold to landing aircraft.
Source: FAA Aeronautical Information Manual · current edition · paragraph 2-1-4.
Research Notes
AIM 2-1-4 covers Runway End Identifier Lights (REIL) — the synchronized white strobes at runway thresholds.
REIL purpose: Help pilots identify the runway in low visibility or against confusing background lighting. Two synchronized white strobes at the threshold, visible from up to 5+ NM.
When most useful: Approaches to runways with bright surrounding lighting (urban areas), competing nearby airports, or unusual airport layouts that make the threshold hard to identify.
Reference: AIM 2-1-4.