Don't confuse PAPI with VASI
The PAPI is a light array positioned beside the runway. It normally consists of four equi-spaced light units color-coded to provide a visual indication of an aircraft's position relative to the designated glideslope for the runway. An abbreviated system consisting of two light units can be used for some categories of aircraft operations. The international standard for PAPI is published by the International Civil Aviation Organisation (ICAO) in Aerodromes, Annex 14 to the Convention on International Civil Aviation, Volume 1, Chapter 5. National regulations generally adopt the standards and recommended practices published by ICAO. An earlier glideslope indicator system, the visual approach slope indicator (VASI) is now obsolete and was deleted from Annex 14 in 1995. The VASI only provided guidance down to heights of 60 metres (200 ft) whereas PAPI provides guidance down to flare initiation (typically 15 metres, or 50 ft).