Who's your Papi? 

Glad you enjoyed it!

Thank you!

Thank you!

Thanks! :)

Thanks, man!

From Wikipedia: "The transition between the two colours must take place over an angle not greater than three minutes of arc. This characteristic makes the color change very conspicuous, a key feature of the PAPI signal. To form the PAPI guidance signal, the color transition boundaries of the four units are fixed at different angles. The lowest angle is used for the unit furthest from the runway, the highest for the unit nearest to the runway. The designated glideslope is midway between the second and third light unit settings." The key thing here is that the angles of the lights are fixed. Therefore, If you go below the so called "Glideslope" (The path you want to have during the approach for landing) your eyes will see not 2 whites and 2 red, but 3 red and 1 white lights. For this to work you need the so called "VMC" - Visual Meteorological Conditions, so If you have a mist you won't be able to see the PAPI lights and you have to use a different approach system. Which is my next project, I'm still working on the name but it will be something like "How do pilots navigate in clouds?" :))