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The highest energy forms in the electromagnetic spectrum are gamma rays (or γ rays) and x-rays, which are dangerous to humans in large quantities. X-rays are energetic enough to travel through the human skin but not quite powerful enough to pass through bone, so they can provide an image of the condition of a patient’s skeleton without the need for invasive surgery. Medical imaging often uses a gamma ray PET scan (which tracks an ingested, radioactive substance) alongside an x-ray CAT scan to provide a three-dimensional view of the patient’s internal physiological systems. 
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Ultraviolet light is more energetic than visible light but is mostly, although not entirely, blocked by the Earth’s atmosphere. The higher energies of ultraviolet light make it more damaging to human skin cells. That is why it is important to wear sunblock on a sunny day to prevent damage to your skin.
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When most people talk about light they usually refer to optical or visible light, because that is what our eyes can perceive. The colors of visible light appears to us as combinations of red, green, and blue. Light bulbs, the Sun, and other stars radiate much of their light energy as visible light.
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Infrared radiation (or thermal radiation) has wavelengths longer than, and energies lower than, visible light. Every body in the universe emits radiation because of its temperature and mostly at infrared wavelengths. Infrared imaging cameras have become useful devices for checking for thermal leaks in a house in order to reduce energy consumption. Infrared goggles are also used on the battlefield at night to detect the thermal radiation from enemy forces. Infrared weather satellites are sensitive detectors of water vapor in clouds—even at night!
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When Heinrich Hertz first showed the existence of electromagnetic waves, he did so using radio waves. Microwaves are used in ovens and mobile phone technology. Radio waves are used for communication with artificial satellites and AM and FM radio broadcasting. The longest wavelengths of radio waves are used to communicate with submarines.
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