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Prisms and Rainbows
Light waves travel through different materials at different speeds. Light travels more slowly through glass of water than through air. When light is traveling through air and enters another material at an angle, the wave of light changes direction. However, different wavelengths or frequencies contained within a beam of white light change at different angles from each other, and you see different wavelengths of light as color. So a white light passing through a prism will make a rainbow. In nature, rainbows occur when sunlight is refracted through rain, or sometimes through a waterfall or even a stream.
The Eye
The eye refracts light waves in order to see. A light wave first enters the eye through the cornea, a clear lens over the top of the eye, which begins to bend the light into focus. The eyeball also contains liquid substances, such as the aqueous and vitreous humors, which also assist with refraction. In an eye with good vision, the light wave comes to a point of focus on the back wall of the eye, or retina, where photoreceptive (light-sensitive) cells capture the light and the image and transmit it to the optic nerve, which takes it to the brain.
Glasses and Vision Correction
If someone's eye is too long or if the lens is more curved than the rest of the eye, the lens bends the light into a focus before it reaches the retina, causing nearsightedness. A short eye or a flat lens causes farsightedness. Astigmatism, a condition in which everything appears blurry, is caused by a cornea that is not completely spherical. This uneven cornea bends the light unevenly. Glasses and contacts use a lens of glass or plastic in front of the eye to refract the light before it reaches the eye and allow the light to reach the retina in focus. Telescopes, cameras and magnifying glasses also use the refraction of light waves.
Refracting other Waves
Refraction of light waves has many practical applications, but other waves also bend and change direction when traveling through different mediums. Waves of the ocean decrease speed and change direction in shallower water, which affects patterns of erosion. When sound waves travel upward from a source to warmer air, the warm air will refract them back towards the Earth. This causes an amplification in the sound and can occur naturally over a cool lake or body of water, where the air close to the ground is cooler than higher air.