The speed of light in the electromagnetic spectrum is constant in a vacuum and is approximately 299,792 kilometers per second (about 3 × 10⁸ meters per second).
This means all electromagnetic waves—whether radio waves, visible light, X-rays, or gamma rays—travel at this same speed when moving through empty space.
However, when electromagnetic waves pass through materials like air, water, or glass, their speed slows down slightly depending on the material’s properties, but in a vacuum, the speed is always the same.