Plain English Meaning

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.

Full 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 .