Speed of light c equals frequency f times wavelength λ.

Total power output is P = σεAT4.
Peak frequency is fpeak = [1011 Hz/K]T.

The energy density u is the time-averaged magnitude of the Poynting vector S divided by the speed of light c. That is, u = I/c. The momentum p carried by light is the total energy U divided by c. Don't confuse the momentum magnitude p with the radiation pressure, which to avoid confusion is written below as F/A.

As a source of light gets less and less intense you can see that the light actually consists of individual particles, called photons.

The first step into a new universe. William Herschel discovers infrared radiation, in 1800.