<Tr> <Th> Near ultraviolet </Th> <Td> 300 </Td> <Td> 1000 </Td> <Td> 3.33 </Td> <Td> 4.15 </Td> <Td> 400 </Td> </Tr> <Tr> <Th> Far ultraviolet </Th> <Td> <200 </Td> <Td>> 1500 </Td> <Td>> 5.00 </Td> <Td>> 6.20 </Td> <Td>> 598 </Td> </Tr> <P> Electromagnetic radiation is characterized by its wavelength (or frequency) and its intensity . When the wavelength is within the visible spectrum (the range of wavelengths humans can perceive, approximately from 390 nm to 700 nm), it is known as "visible light". </P> <P> Most light sources emit light at many different wavelengths; a source's spectrum is a distribution giving its intensity at each wavelength . Although the spectrum of light arriving at the eye from a given direction determines the color sensation in that direction, there are many more possible spectral combinations than color sensations . In fact, one may formally define a color as a class of spectra that give rise to the same color sensation, although such classes would vary widely among different species, and to a lesser extent among individuals within the same species . In each such class the members are called metamers of the color in question . </P>

The color of visible light can be determined by frequency or