Expand the acronyms and you get your answer:
Precision Approach Path Indicators and Visual Approach Slope Indicators. They are parts of an overall approach lighting system that also includes approach lights as such. And one only uses them when on approach.
FAA regulates them with other approach lights (including REILs) - with a separate section for airfield lights (beacons, runway lights, taxiway lights, obstruction lights, illuminated wind indicators, etc.)