The human eye and brain work together to convert visible light energy into an electrical impulse that can be interpreted as an image--allowing us to see what we need to see to survive.

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  • 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. 

  • Term Part of Speech Definition Encyclopedic Entry
    cornea Noun

    transparent anterior part of the external coat of the eye covering the iris and the pupil and continuous with the sclera.

    electromagnetic spectrum Noun

    continous band of all kinds of radiation (heat and light).

    iris Noun

    the contractile, circular diaphragm forming the colored portion of the eye and containing a circular opening, the pupil, in its center.

    lens Noun doubly convex, transparent body in the eye, situated behind the iris, that focuses incident light on the retina.
    nanometer Noun

    (nm) billionth of a meter.

    photoreceptor Noun

    specialized cell that is sensitive to light.

    pupil Noun

    the contractile aperture in the iris of the eye.

    retina Noun

    sensitive tissue at the back of the eye that receives images and sends signals to the brain about what is seen.

    visible light spectrum Noun

    light and colors that can be seen by human beings.


This material is based in part upon work supported by the National Science Foundation under Grant No. DRL-0840250. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.

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