Runway edge lighting systems outline the edge of runways during nighttime and reduced visibility conditions. Runway edge lights are classified by intensity, high intensity (HIRL), medium intensity (MIRL), and low intensity (LIRL). LIRLs are typically installed on visual runways and at rural airports. MIRLs are typically installed on visual runways at larger airports and on nonprecision instrument runways, HIRLs are installed on precision-instrument runways.
Recommended standards for the design and installation of runway edge lighting systems are published by the FAA and are contained in ICAO . These light fixtures are usually elevated units but semiflush lights are permitted. Each unit has a specially designed lens which projects two main light beams down the runway. Elevated runway lights are mounted on frangible fittings and project no more than 30 in above the surface on which they are installed. They are located along the edge of the runway not more than 10 ft from the edge of the full-strength pavement surface. The longitudinal spacing is not more than 200 ft. Runway edge lights are white, except that the last 2000 ft of an instrument runway in the direction of aircraft operations these lights are yellow to indicate a caution zone. A typical layout of low-intensity and medium-intensity runway edge
lights is shown in below Fig.
If the runway threshold is displaced, but the area that is displaced is sable for takeoffs and taxiing, the runway edge lights in the displaced area in the direction of aircraft operations are red, .