Back when, flying commercial, it was a rule to "light up" the aircraft as you descended below 10,000 ft. That meant, all lights on, including landing lights, for mid-air collision avoidance reasons. It is not a bad idea to "light up" approaching class D airspace so the tower can see you. We also found out that if the landing lights, located on the main gear, had the filaments mounted horizontally the potential for blowing out the light on landing was considerable. Mounting the landing light so the filament was vertical solved a lot of problems. Bart
