Definition
White lights placed along the sides of a runway to outline its edges to pilots during night operations and low-visibility conditions. They are classified by intensity as high intensity runway lights (HIRL), medium intensity runway lights (MIRL), or low intensity runway lights (LIRL). On instrument runways, the last 2,000 feet (or half the runway length, whichever is less) are yellow when viewed from the landing direction, indicating the caution zone before the departure end.
Plain English
The line of white lights running down both sides of the runway so a pilot can see exactly where the runway begins, ends, and how wide it is at night or in poor visibility.
Context Anchor
Pilots use runway edge lights during night approaches, landings, takeoffs, and taxi operations near an active runway.
Why Pilots Care
They give immediate visual confirmation of runway width and alignment, preventing runway excursions during night and reduced-visibility operations.
Intuition Check
Do not confuse runway edge lights with lights that mark the runway centerline or the runway end. Runway edge lights mark the left and right sides of the usable runway surface.
Example Sentence 1
On final approach at night, the pilot used the runway edge lights to line up with the center of the runway.
Example Sentence 2
As the plane rolled out, the runway edge lights changed from white to yellow, indicating the end was near.