Which types of electromagnetic waves travel at the speed of light?

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All forms of electromagnetic radiation travel at the speed of light when moving through a vacuum. This universal constant is defined as exactly 299,792,458 metres per second.123

Rather than being limited to a single type, this speed applies to the entire electromagnetic spectrum, which encompasses all of the following:14

Radio waves (including commercial radio, television, and radar)15
Microwaves14
Infrared radiation15
Visible light14
Ultraviolet radiation14
X-rays14
Gamma rays12

While these waves differ significantly in their frequency, wavelength, and energy levels, they all share the same fundamental propagation speed in a vacuum. In quantum theory, this also applies to photons, which are the energy packets that constitute electromagnetic radiation.124