Runway lighting systems are separated into categories based on their specifications. This range of specifications includes lighting intensity.
On runways that are equipped for night operations and low visibility weather conditions, there will be a series of runway intensity lighting settings available.
The intensity settings can be controlled by the Air Traffic Control (ATC) tower or in some instances by pilots in approaching aircraft.
Pilots of approaching aircraft that require the activation of runway lights or the adjustment of intensity lighting can do so by requesting it via ATC.
At uncontrolled airports, this may be activated if a PCL system is installed to the Approach Lighting System (ALS).
Known as Pilot Controlled Lighting (PCL), this system is commonly found at airports that have restricted ATC operating hours or at uncontrolled airports.
PCL can be activated by the pilot holding down the communications microphone for several seconds. Once the UNICOM frequency is selected (122.80), this will allow for the runway lighting to be activated and the intensity setting to be selected.
Depending on weather conditions and time of day, the High-Intensity Runway Lights (HIRL) setting may be selected.
Under HIRL conditions, the following runway light configuration will be selected:
- Runway edge lights must not exceed 200 feet in separation.
- There must be centerline lights every 30-50 feet for the entire runway.
- Runway lights are white until the approaching aircraft is at 1,000 feet, in which they then transition to a solid red color.
- Runway edge lights must be installed within 10 feet off the paved surface of the runway.
While the exact Approach Lighting System (ALS) differs from airport to airport, the HIRL systems typically offer a much more versatile solution to various operations.
HIRL are most commonly found at large, major international airports which facilitate CAT II and CAT III instrument approach procedures.
In the United States, it is an FAA requirement for a runway to be equipped with HIRL for CAT II and CAT III operations.
Approach Lighting Systems such as HIRL and various other aerodrome lighting have commonly been made of halogen material, however, this has recently been shifting at some airports towards an LED-based runway lighting system.
Advantages of an LED-based system include lower operating temperatures of HIRL systems along with lower and more efficient energy levels required to power the system.
LED bulbs also typically have a longer operational lifespan, in which studies have shown that they last 5-10x longer than halogen bulbs.