It basically work as a warning to helicopter or plane pilots. A tower is much taller. Can be up to 200 meters from the ground. As a result, when a plane or a helicopter flies through the sky, if it collides with the tower for some reason, it can be a big danger. Therefore, the use of such lights in such cases is a government rule in many country . It is not just for mobile towers but any type of tower or high-rise installtion.
Why only red light is used?
Firstly, the color red is used as a warning or danger sign. Second, the wavelength of red light is much longer. So it can be seen in smoke, fog or dust. Moreover, it is more important in the night sky, so it will appear in the dark. These are the reasons for the use of red.