by Matthew Johnson

Created on: May 14, 2009   Last Updated: January 08, 2012

The short answer to the question posed in the title is no, the human eye cannot, in most cases, see ultraviolet light. In order to understand why, we must first look at the functions and qualities of light. Light is a form of electromagnetic energy that exists in a wide range of colors known as a spectrum. It ranges from infrared at the high end of the spectrum all the way down to ultraviolet at the low end. We see an excellent example of the visible colors in the light spectrum every time we look at a rainbow. Those visible colors are red, orange, yellow, green, blue, indigo, and violet and all the color combinations in between.

Light is measured using a term called wavelength. In order to visualize what wavelength is, drop a pebble in a calm body of water. The pebble produces a series of waves that radiate from the center. Wavelength is the measurement of the distance between these waves. Light is, of course, measured on a much smaller scale. The wavelength of light is measured using a unit of measurement called nanometers, commonly abbreviated as nm, which are actually one billionth of a meter each. The visible spectrum of light ranges from 700 nanometers at the red side of the spectrum, to 400 nanometers at the violet end of the spectrum. All light wavelengths beyond these two ranges (meaning above 700nm or below 400nm) are not visible to the human eye. The ultraviolet spectrum ranges between 10nm and 400nm.

Next, we should look at how the human eye functions. The back of the eye, known as the retina, contains three types of cells that detect light. These cells are known as photoreceptors. The first type of these photoreceptors are called rods. Rods function in low light and are the cells responsible for night vision. The second type are known as cones. Cones are cells responsible for daytime vision. The third type of cells are known as photosensitive ganglion. These are the cells responsible for the reflex response of the pupil when exposed to bright light.

Cone cells are the primary photoreceptor responsible for the eye's detection of color. There are some who have a malfunction in these cells which results in certain types of color blindness. As stated above, the human eye can only see lights that are in between the infrared and ultraviolet wavelengths. Cones are further divided into 3 types. The first type, known as L cones, detect light of long wavelength, the second type, known as M cones, detect light of a medium wavelength and the third, known as

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