RGBA forms a vector indicating the direction the light points. See PluginsAndObjects for how this works.
RGB color is set to white. Alpha is set to brightness or 0 for off.
This light is off if the runway lights are inoperative or airport lights are off (day-time VFR conditions).
The airport beacon forms a directional light, useful for airport beacons, which turns off at times appropriate for airport lgihts.