All  spectroradiometer models are capable of measuring the photon flux and the energy flux across the reported wavebands. This figure at right shows the difference between photon flux and energy flux.  Click for larger view.

The figure below shows a relative increase in UV and blue photon flux near solar noon and a shift to a greater relative proportion in near infrared photon flux in the morning and evening.

In the next graph below, waveband ratios from the above sun spectra were calculated to further illustrate the spectral shift of the sun through the day as the zenith angle changes.