Schematic diagram of longitudinal section through <a href="https://en.wikipedia.org/wiki/Precision_approach_path_indicator" class="extiw" title="w:Precision approach path indicator">PAPI</a> (Precision approach path indicator)<br>
1 = Axis datum<br>2 = Light source<br>3 = Filter-red<br>4 = Lenses<br>5 / 6 = Light beam- white/red
<a href="//commons.wikimedia.org/wiki/User:LezFraniak" class="mw-redirect" title="User:LezFraniak">LezFraniak</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>