Flashing green and white lights in the USA from the air

[JohnnyRocket]

When flying at night in the USA I often notice bright alternate flashing green and white lights coming from airfields on the ground.

What exactly is the point of these flashing lights?

They are obviously quite powerful as they can be seen from some distance away.

Are the green and white lights spaced at specific intervals to indicate specific airports or is it not as deliberate as this?

[mcgoo]

It means the type of airfield:

White and green: lighted land airport
White and yellow: lighted water airport
green, yellow and white: lighted heliport

Theres different combinations to include military etc, when lit at class b,c,d and e airports in the day it is an indication of IFR conditions.

[Rainboe]

It's a relic from the old days when your head would be sticking up out of the cockpit of your HP42, desperately scanning for the grass airfield you were going to be landing on. It helped to have something distinguishing your grass airfield from the grass field next door with winter wheat. So they put a rotating beacon on the tower flashing airport ID. Nobody even looks for them anymore....it's all inertial navigation. So boring.

[Avman]

In the good old days, when we ATC people were often invited to the front office, I recall a number of instances of sighting Birmingham´s beacon quite some way out (well over 80 miles) on a gin clear night. Incidentally, does it still exist?

[retflyboy]

If the rotating beacon is on during daylight hours it means the airfield is IFR; that is below VFR minimums.

If you see the white portion as one single flash (blip) it is a civilian airfield; If it goes blip-blip that is two flashes, it is a military airfield.

The rotating beacon does not identify the airfield, no morse code or any such.