Approach Light Systems (ALS) aid pilots on instrument approach in transitioning from instrument to visual flight for landing.
Depending on the specific approach lighting system used, the lights will begin at the landing threshold of the runway and extend into the runways approach area anywhere from 1,500 feet to as much as 3,000 feet. Some systems include sequenced flashing lights which have the appearance of a ball of light traveling toward the runway.
The graphic below illustrates the appearance of the different types of approach lighting systems you may encounter.
