Light is only a small part of a much larger family. The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. They are all electromagnetic radiation, differing only in wavelength and frequency. Radio waves have the longest wavelengths, from meters to kilometers. Gamma rays have the shortest, less than a picometer. The visible spectrum, which human eyes can detect, sits in the middle, from about 400 to 700 nanometers.

Each region of the spectrum has its own properties and uses. Radio waves carry broadcast signals and Wi-Fi. Microwaves heat food and carry radar. Infrared is felt as heat and used in night vision. Visible light is what we see. Ultraviolet causes sunburn and is used in sterilization. X-rays pass through soft tissue and image bones. Gamma rays are the most energetic, produced by nuclear decay and cosmic events. The atmosphere blocks most of the spectrum, which is why astronomers put telescopes in space. The James Webb Space Telescope observes in infrared, because infrared passes through dust that blocks visible light.

Spectrum regions

• Radio. Longest wavelengths, communication.
• Microwave. Radar, heating, cosmic background.
• Infrared. Heat, night vision, astronomy.
• Visible. What the human eye sees.
• Ultraviolet. Sunburn, sterilization.
• X-ray. Medical imaging, crystallography.
• Gamma. Nuclear decay, most energetic.

The electromagnetic spectrum is not the same as the visible spectrum. Visible light is a small slice of the whole.