Actually, the electromagnetic spectrum can be expressed in terms of energy, wavelength, or frequency. Each way of thinking about the EM spectrum is related to the others in a precise mathematical way. So why do we have three ways of describing things, each with a different set of physical units?
imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.h... imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
More about the Electromagnetic Spectrum ... As it was explained in the Electromagnetic Spectrum - Level 1 of Imagine the Universe!, electromagnetic radiation can be described in terms of a stream of photons, each traveling in a wave-like pattern, moving at the speed of light and carrying some amount of energy.
imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.h... imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html
Electromagnetic spectrum - Wikipedia, the free encyclopedia
The  electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic...
en.wikipedia.org/wiki/Electromagnetic_spectrum
The Electromagnetic Spectrum ... Click on any part of the spectrum for further detail. ... Speed of light...
hyperphysics.phy-astr.gsu.edu/hbase/ems1.html
Regions of the Electromagnetic Spectrum ... The electromagnetic spectrum is the distribution of electromagnetic radiation according to energy (or equivalently, by virtue of the relations in the previous section, according to frequency or wavelength).
csep10.phys.utk.edu/astr162/lect/light/spectrum.html csep10.phys.utk.edu/astr162/lect/light/spectrum.html
This page is all about electromagnetic waves. The visible spectrum is just one small part of the electromagnetic spectrum. These electromagnetic waves are made up of two parts. The first part is an electric field.
www.purchon.com/physics/electromagnetic.htm www.purchon.com/physics/electromagnetic.htm
The Electromagnetic Spectrum ... The electromagnetic spectrum is a continuum of all electromagnetic waves arranged according to frequency and wavelength. The sun, earth, and other bodies radiate electromagnetic energy of varying wavelengths. Electromagnetic energy passes through space at the speed of light in the form...
www.geo.mtu.edu/rs/back/spectrum/ www.geo.mtu.edu/rs/back/spectrum/
The electromagnetic spectrum is a vast band of energy frequencies extending from radio waves to gamma waves, from the very lowest frequencies to the highest possible frequencies. The spectrum is arranged by the frequency of its waves, from the longest, lowest energy waves to the shortest, highest energy waves.
www.spacetoday.org/DeepSpace/Telescopes/GreatObservator... www.spacetoday.org/DeepSpace/Telescopes/GreatObservatories/Chandra/ElectromagneticSpectrum.html
What are electromagnetic waves ? ... Light, microwaves, x-rays, and TV and radio transmissions are all kinds of electromagnetic waves. They are all the same kind of wavy disturbance that repeats itself over a distance called the wavelength.
www.colorado.edu/physics/2000/waves_particles/index.htm... www.colorado.edu/physics/2000/waves_particles/index.html