Table of Emissivity Request
A factor common to both the Stefan-Boltzmann Law and Planck’s Equation is the term “emissivity”. Emissivity is the propensity of an object or surface to absorb and emit infrared radiation. It can be expressed as the ratio of the radiant energy emitted by an object at a temperature T and the radiant energy emitted by a blackbody at the same temperature.
An object that absorbs all the IR energy that falls on it and re-radiates all the IR energy it absorbs is termed a perfect blackbody, and is given an arbitrary emissivity value of E = 1.0. Perfect blackbodies do not exist in nature. The degree to which materials approximate to an emissivity of 1.0 is a function of their molecular construction and their surface characteristics, i.e. rough, pitted, highly polished and their geometries i.e. flat, conical, spherical etc. Emissivity is also affected by the angle at which the IR energy strikes the surface, i.e. the closer to perpendicular the higher the apparent emissivity. Emissivity is wavelength and temperature dependent. Typically for metals, the emissivity is higher at shorter wavelengths near the visible spectrum. Our emissivity table provides values for the total emissivity of various material surfaces and emissivities that are specific to a particular wavelength at different temperatures.