If light waves were infinitely long, it would imply that their wavelengths would be infinitely large. In practical terms, this would mean that the frequency of the light waves would approach zero.
The frequency of a wave is inversely proportional to its wavelength. As the wavelength increases, the frequency decreases, and vice versa. In the case of infinitely long light waves, the frequency would tend toward zero, which implies that the waves would oscillate extremely slowly or not oscillate at all.
In our current understanding of physics, light waves with zero frequency do not exist. The frequency of light is directly related to its energy, and if the frequency were zero, it would mean that the light wave carries no energy. Light waves with no energy would not be able to interact with matter or be detected by our eyes or any other instruments.
Moreover, the speed of light is determined by the properties of the medium through which it propagates. In a vacuum, the speed of light is constant, regardless of the wavelength. If the wavelength of light waves were infinitely long, it would not affect the speed of light.
In summary, if light waves were infinitely long, they would have a frequency approaching zero, carrying no energy, and would be undetectable. However, this scenario is not consistent with our current understanding of light and electromagnetic radiation.