The Planck–Einstein relation relates the energy of a photon to its wavelength:
E = h*ν = h*c/λ
where ν is the frequency of the photon,
λ is its wavelength,
c is the speed of light in a vacuum, and h is Planck's constant = 6.626*10^(-34) J*s
In this case, the energy of a photon with a wavelength of 6200nm is equal to:
E = .(6.626*10^(-34) J*s)*(2.998*10^8 m/s)/(6200*10^-9 m)
E = 3.20*10^(-20) J
