



Units of Wavenumbers (click on equations to view enlarged)
Yet a third spectral unit, commonly used in spectroscopy, is wavenumber, the number of waves per cm: σ = ν /100c cm^{1}. Converting (1) to these units gives
. (13)
Again, the peak is where the derivative with respect to wavenumber vanishes:
so . (14)
The peak value is
. (15)
The spectral photon radiance is found by dividing L_{σ} by the energy of a photon, 100hcσ :
. (16)
We next find the wavenumber at the peak of the spectral photon radiance:
and . (17)
The peak spectral photon radiance is
. (18)
Fig. 3 shows plots of L_{σ} and L_{σ}^{P} for various temperatures. Note again the important difference between the spectral radiance and spectral photon radiance.
Fig. 3  Spectral radiance, L_{σ }, (top) and the spectral photon radiance, L_{σ}^{P}, (bottom) as a function of wavenumber, σ, for various temperatures. The small black dots indicate the wavenumber and value of the peak, at 10 K temperature intervals. Note that L_{σ} and L_{σ}^{P} have different wavenumber dependences. Although the peak wavenumber is proportional to T for both quantities, L_{σ} peaks at a higher wavenumber than L_{σ}^{P}. Furthermore, the peak value of L_{σ} increases as T ^{3}, whereas the peak value of L_{σ}^{P} increases as T ^{2}.

Gascell Simulator 