Note 1 to entry: The photon spherical irradiance can be expressed by

$E_{\text{p}\text{,o}}={\displaystyle \underset{4\pi }{\int }{L}_{\text{p}}\text{d}\Omega }$

where Ω is solid angle and L_p is photon radiance.

Note 2 to entry: The photon spherical irradiance is expressed in second to the power minus one per square metre (s⁻¹·m⁻²).