Definition
A runway edge lighting system set to a medium brightness level, used to mark the lateral edges of the runway during night operations or low-visibility conditions. The lights are white and define the usable landing and takeoff surface, with the last 2,000 feet (or half the runway, whichever is less) appearing yellow when viewed from the landing direction.
Plain English
A row of medium-brightness white lights along each side of the runway that show the pilot where the runway edges are at night or in poor visibility.
Context Anchor
Seen in airport information, runway descriptions, night flying, and approach planning.
Why Pilots Care
They supply the minimum lighting needed for safe night and low-visibility takeoffs and landings at airports that do not have high-intensity systems.
Intuition Check
“Medium intensity” does not mean the pilot may treat the runway as only moderately lit in all conditions. It is a lighting-system category; actual usefulness still depends on weather, visibility, and whether the lights are operating.
Example Sentence 1
The chart supplement showed the field had MIRL on Runway 27, activated by clicking the mic seven times on CTAF.
Example Sentence 2
MIRL provide enough illumination for the runway edges at many general aviation airports.