isplays use blue, red, and green light sources to generate color. ULTRAVIOLET In an era where many people are concerned about ozone depletion, ultraviolet radiation has received a significant amount of publicity. Most of us associate ultraviolet radiation with sunburn and Chapter Two Green Figure 2.8 The color triangle, which is attributed to James Clerk Maxwell, illustrates how the three receptors in the human eye respond to different wave- White Yellow lengths. Magenta the potential occurrence of skin cancer. Technically, ultraviolet radiation represents that portion of the electromagnetic spectrum above visible light. Thus, ultraviolet radiation has a shorter wavelength and higher fre- quency than does visible light. The wavelength of ultraviolet radiation ranges from approximately 400 billionths of a meter to about 10 billionths of a meter. Ultraviolet waves are generated by the sun, and the ozone layer blocks most of those rays. This explains why the depletion of the ozone layer in the earth's atmosphere is a great matter of concern. Another source of ultraviolet radiation is ultraviolet lamps that many persons associate with tanning salons. However, ultraviolet light is also used in hospitals to treat skin conditions and kill different types of bacteria. X RAYS As we move up the ladder of the frequency spectrum, we find high-energy waves, referred to as X rays, residing above the ultravi- olet band. X rays were discovered by Konrad Röntgen in 1895 when he determined, by accident, that a fluorescent plate glowed even when it was far away from a tube conveying an electron beam. When he placed his hand in front of the fluorescent plate, he was able to see the bones in his hand; this discovery paved the way for the use of X rays in such diverse applications as inspecting welds in pipes and checking body parts. Understanding Light The wavelength of X rays ranges from approximately 10 billionths of a meter to about 10 trillionths of a meter. Thus, X rays are electromag- netic waves with shorter wavelengths than t