Barry Rice

- doing science on a terrestrial planet -

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Types of photons

Photons are classified into broad categories delineated by their wavelengths. This is equivalent to classifying them by how much energy they have, as I explained in the previous section.

As you probably noticed, scientists use different units of measurement for the wavelengths of different types of photons. This is because photons vary over such a wide range of wavelengths that units appropriate for one kind of photon wavelength are annoying for another kind of photon. (Consider, for example, the clumsiness in specifying the wavelength of a radio wave as 100,000,000,000 nm, or an ultraviolet photon as 0.001 microns. These would be better written as 100 m and 1 nm, respectively.)

Conversions among the commonly used units (especially microns and nanometers) are:

1 meter=106 microns,
1 mm=103 microns=106 nanometers,
1 mm=107 angstroms.


4 February 2009