Do you know the light gun signals that are used in case of a radio failure or if your aircraft is not equipped with a radio?
Air Traffic Control (ATC) will use a signal lamp to give you instructions and clearance limits. The light gun has a focused bright beam and is capable of emitting three different colors: red, white and green.
You have to look closely but they are visible from a surprising distance away. These colors may be flashed or steady, and have different meanings to aircraft depending if you are in flight or on the ground.
Pilots can acknowledge the instructions by "rocking" their wings, moving the ailerons if on the ground, or by flashing their landing or navigation lights during hours of darkness.
Here's a quick refresher to the signals used...