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.
Please complete the form below to obtain your free copy the Process
Sensor's Table of Emissivity.
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