If light waves had no amplitude, it would mean that the electric and magnetic fields comprising the light wave would have zero magnitude. In practical terms, this would imply that there is no oscillation or variation in the intensity of the light wave.
Since the amplitude of a light wave determines its intensity or brightness, a light wave with no amplitude would essentially be invisible. It would not be detectable by our eyes or any light-detecting instruments.
In addition, the absence of amplitude would also mean that there would be no energy associated with the light wave. Light waves carry energy in the form of photons, and the intensity of the wave is directly related to the energy carried by each photon. Without amplitude, the light wave would not transfer any energy or have any impact on the objects it interacts with.
Essentially, if light waves had no amplitude, it would result in the absence of visible light and its associated properties.