This Demonstration plots the radiated heat in

or

from a hot body having a given emissivity,

, as a function of its temperature and that of its surroundings, both entered either in °C or °K. This heat output is calculated with the Stefan-Boltzmann law,

, where

is the emissivity,

is the Stefan-Boltzmann constant,

is the area in

(equal to 1 in this Demonstration),

is the radiating body temperature, and

is the ambient temperature, both in °K. The upper graphic is a schematic visual representation of the selected emissivity (not to scale).
Reference: C. J. Geankoplis,
Transport Processes and Unit Operations, 
ed., Boston: Allyn and Bacon, 1983.