# Q & A: Lowest energy color of visible light

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Most recent answer: 10/22/2007
Q:
What color of visible light has the lowest energy?
- Anonymous
A:
We guess that you’re asking about the energy in each ’photon’- a blip of light energy typically absorbed in a single step when light hits some material. The total energy in the light wave can be big or small for any color, but this single-photon energy is fixed for a given color.

On the low end of the visible frequency spectrum is red, and on the high end it's violet.  The energy per photon is proportional to the frequency of the light, and that constant of proportionality is Planck's constant.  We write

E = h*f

where f is the frequency of the light in Hz, and h is 6.626E-34 Joule-seconds.

There are electromagnetic waves of longer wavelength and lower frequencies than red light, and they have lower energies per photon than red light, but we are not able to detect them with our eyes.

Tom (+ mike)

(published on 10/22/2007)