Linked from
The 17 pages that link to Radiant flux, each with the reason it gives.
Stefan–Boltzmann lawRelated: The law gives emitted radiant flux per unit surface area.
TransmittanceRelated: Flux measurements can provide the numerator and denominator of transmittance.
Luminous efficacyRelated: It supplies the radiometric power compared with visually weighted output.
RadiometryRelated: It is the power whose distribution across wavelength an SPD describes.
Solar radiationRelated: It expresses total solar energy flow before dividing by an area.
CandelaRelated: Photometry converts radiant flux into visually weighted quantities such as candela.