The type of fixtures used on a runway is dependent its category, CATI, CAT II, CAT III, and these application dependent on location can either be inset or elevated.
Runway edge lights are generally steady white lights that show the edge or the usable part of a runway. On instrument runways, the white lights will change to yellow when approaching the end of the runway length , and then they turn red as the aircraft reaches the end of the runway.
There are several categories of runway edge lighting, high-intensity (HIRL), medium-intensity (MIRL) or low-intensity (LIRL) all of which are designed to meet different criterial of international standards.
Runway Centerline Lighting System (L-850A) – On precision runways, a runway centerline light system is installed, with white lights spaced at pre-determined intervals on the centerline of the runway. Towards the end of the runway the coding of the lights change to alternate red and then all red, thus indicating to pilots, the length of runway remaining.
Touchdown Zone (TDZ) (L-850B) Lighting must be provided on runways available for use in low visibility conditions so as to provide enhanced identification of the touchdown area. The method of provision is specified in ICAO Annex14 and the lighting must extend from the landing threshold for either 900 meters or to the midpoint of the runway, whichever is the least