If you see a green flashing light outside of an airplane window, it is likely an aviation navigation light. Aircraft use various lights to enhance visibility and indicate their position to other aircraft and ground observers. Here are a few possibilities for a green flashing light:
Green navigation light: Aircraft typically have navigation lights on their wings, with the right wingtip featuring a green light. These lights help pilots and observers determine the orientation and direction of an aircraft.
Wingtip strobe light: In addition to steady navigation lights, some aircraft have strobe lights on their wingtips. Strobe lights emit intense, brief flashes of light, and they are often white. However, in certain cases, aircraft may feature colored strobe lights, including green.
Anti-collision light: Another possibility is an anti-collision light, which is a bright, flashing light installed on aircraft to improve their visibility and reduce the risk of collisions. Anti-collision lights can be either white or colored, and green is one of the possible colors used.
The specific light pattern and color depend on the aircraft's design, type, and operational requirements. Green lights are generally associated with the right side of an aircraft. The flashing nature of the light is meant to attract attention and help differentiate the aircraft from other lights in the vicinity.
If you observe such a light while on an airplane, it is likely just a standard navigational or anti-collision light. It is part of the aircraft's lighting system and serves as a safety measure, ensuring that the aircraft is visible to other pilots and air traffic controllers, especially during low-light conditions or at night.