Electromagnetic waves, including visible light, radio waves, microwaves, and X-rays, do not have an inherent upper limit of amplitude. The amplitude of an electromagnetic wave represents the maximum displacement of the electric or magnetic field from its equilibrium position. It is typically measured as the magnitude of the electric or magnetic field strength.
In theory, the amplitude of an electromagnetic wave can be arbitrarily large. However, in practice, there are limitations imposed by the physical properties of the sources generating the waves and the materials they interact with. For example, if the amplitude of an electromagnetic wave becomes extremely large, it can cause significant heating, ionization, or other damaging effects on matter.
In the context of everyday electromagnetic waves, such as those used for communication and in our environment, the amplitudes are typically quite small. The amplitudes are usually measured in terms of electric or magnetic field strength, which can vary depending on the specific application or situation.