Approach Light System (ALS)

"An approach lighting system, or ALS, is a lighting system installed on the approach end of an airport runway and consists of a series of light bars, strobe lights, or a combination of the two that extends outward from the runway end. ALS usually serves a runway that has an instrument approach procedure (IAP) associated with it and allows the pilot to visually identify the runway environment once he or she has arrived at a prescribed point on an approach.

The most common approach light system configurations include:

• MALSR: Medium-intensity approach light system with Runway Alignment Indicator Lights
• MALSF: Medium-intensity approach light system with Sequenced Flashers
• SALS: Short approach light system
• SSALS: Simplified Short approach light system
• SSALR: Simplified Short approach light system with Runway Alignment Indicator Lights
• SSALF: Simplified Short approach light system with Sequenced Flashers
• ODALS: Omnidirectional approach light system
• ALSF-1: Approach light system configuration 1
• ALSF-2: Approach light system configuration 2
• CALVERT I/ICAO-1: ICAO-compliant configuration 1
• CALVERT II/ICAO-2: ICAO-compliant configuration 2
• LDIN: Lead-in lighting'

Quoted from Wikipedia