X-rays are a form of radiation similar to light rays, except that they are more energetic than light rays and are invisible to the human eye. They are created when an electric current is passed through a vacuum tube. X-rays were accidentally discovered in 1895 by German physicist Wilhem Roentgen (1845-1923), who was later awarded the first Nobel Prize in physics for his discovery. Roentgen was also a photographer and almost immediately realized that the shadows created when x-rays passed through the body could be permanently recorded on photographic plates. His first X-ray picture was of his wife’s hand. Within a few years, X-rays became a valued diagnostic tool of physicians world-wide.

Check where the X-rays fall in the electromagnetic spectrum. They have a higher frequency than visible light. Higher frequency results in higher energy. The higher energy of the X-ray photons is the reason why their properties differ from that of the visible light that we are accustomed to.

Source: Nick Simons Institute content ‘X-rays’

As mentioned, the frequency of X-rays is higher than that of visible light. And hence, they are able to penetrate our tissues and cells unlike the usual visible light. However, these X-rays are not able to penetrate our bone cells. This is why X-rays are so useful! Because they cannot penetrate the bone cells, the bones in the body create a shadow (the white part in an X-ray image) on the photographic X-ray film, whenever the body is exposed to X-rays.