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Roger Weller, geology instructor                     

Fluorescent Minerals
Steve Tyminski
Physical Geology
Fall 2007

                                                  Visible Light  

          Visible light makes-up only a tiny fraction of the entire electromagnetic radiation spectrum.

The visible light band contains only the range of frequencies which the human eye can see.  The wavelengths that humans are able to see is a very narrow range between approximately 400 and 700 nanometers, the remainder of the electromagnetic spectrum is invisible.


light wavelength

Courtesy: Microscopy Resource Center


          Relating specific colors to a region of wavelength defines the colorís different tones, hues, and shades. Itís possible for many different situations to produce identical colors. For example, a yellow color may be caused by a single wavelength of  590 nanometers, or may be the result of two equal amounts of light having individual wavelengths of 580 and 600 nanometers (580 + 600 ł 2 = 590).  The possibility of viewed color coming from multiple wavelengths is much greater than color coming from a single wavelength.


light sources figure

Courtesy: Microscopy Resource Center


          The wavelength of the emitted light depends on how much energy is released, which depends on the particular position of the electrons of the atoms of the material. Consequently, different sorts of atoms will release different sorts of light photons. In other words, the color of the light is determined by what kind of atom is excited.  This is the basic mechanism at work in nearly all light sources with the only significant main difference being between the process of exciting the atoms.

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