Waves of electromagnetic energy traveling across the globe and throughout space make life on Earth possible. Activities like reading a computer screen, calling someone on a cell phone, heating up hot chocolate in a microwave, or using a GPS device would be impossible without electromagnetic energy.

Different types of electromagnetic energy are characterized along a spectrum according to their wavelengths and how much energy they possess. The electromagnetic spectrum ranges from longer wavelength, lower energy waves, like microwaves and radio waves, to shorter wavelength, higher energy waves, like X-rays and gamma rays. Visible light waves are the only wavelengths of the electromagnetic spectrum that humans can see. The different wavelengths of visible light are seen as the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet. The longest wavelengths (around 700 nanometers) are red and the shortest wavelengths (380 nanometers) are violet.

The human eye and brain work together to convert visible light energy into an electrical impulse that can be interpreted as an image. When focusing on an object, the cornea, iris, and pupil help light enter the lens of the eye. The lens bends the light so the image is turned upside down and projected onto the retina at the back of the eye. This stimulates the retina’s photoreceptors, called rods and cones. Cones detect color and fine details in high light conditions. In low light conditions, rods detect grays and movement. Together, rods and cones convert the light hitting the retina into an electrical impulse that is carried from the eye to the brain via the optic nerve. Then the occipital, temporal, and parietal lobes of the brain process the information and interpret the image being seen.