Heat, light, radio waves, and x-rays are all forms of energy. The difference between the various forms of energy depends on the wavelength of the energy waves. Radio waves, for instance, have a very long wavelength, while x-rays have a very short wavelength.
We can see only a very small portion of the energy waves around us. What we can see is .called visible light. The visible light with the shortest wavelength appears as deep violet, while visible light with the longest wavelength appears as deep red.
But there are energy waves that are not seen, yet can be felt. For example, energy waves with a wavelength slightly longer than the wavelength of the deepest red are called infrared waves. We can’t see them, but we can feel them as heat.
And energy waves with a wavelength slightly shorter than those of deep violet are called ultraviolet waves. We can’t see them either, but we can feel their effects on our skin when we get sunburned.