[Richard777 (OP)]

An active emitter shines light and heat into local space. A force may be associated with the emitter and another force may be associated with the emitted radiation.

Each force may be represented as a vector. Each vector is four dimensional. If three “radiant conditions” apply, then the components of force will give the Stephan-Boltzmann equation of brightness.

Reference attached.

[alancalverd]

Full marks for neatness.