This study is a follow-up investigation of the simultaneity of physical phenomena based on the speed-limit structure , and examines whether this structure also holds in the domain of classical electromagnetic waves.Using the refractive index as the central variable, the relationships among the wavenumber, wavelength, frequency, and energy transport characteristics are analyzed from the perspective of the speed-limit structure.From the derived analytical relations, it is shown that the principal physical quantities describing electromagnetic waves form a mutually constrained structure determined by the partition between and under the constraint of the limiting speed .