What is emissivity and why is it important?
What is emissivity and why is it important? |
 | Emissivity is a measure of how effectively a surface can emit energy as thermal
radiation. Surfaces can have an emissivity value ranging from 0 to 1.0 with 0 being a perfect
reflector and 1.0 being a perfect black body radiator (a black body radiator is an object that
absorbs all incoming radiation and does not reflect any, and then radiates out energy at the same
rate that it receives it). As a general rule, as an object becomes more reflective, the emissivity
value goes down. For example, shiny aluminium has an emissivity value of 0.05 whereas paint has a
typical emissivity value of 0.95. In summary, emissivity can be thought of as the ratio of the
effectiveness of the surface to emit thermal radiation compared to a perfect black body
radiator. | |||||||||||||||||||||||||||||
Below is a chart of some emissivity coefficients of commonly measured items.
As you can see, a majority of commonly measured items have emissivity values close to
0.95 which is why this is often set as the default. However to get the highest accuracy results, it
is important to adjust the emissivity setting on your infrared thermometer to match what you are
measuring.
What if you need to measure something like aluminium but you don’t have an adjustable
infrared thermometer?
If you need to measure something with a low emissivity coefficient, then you can stick some black electrical tape on what you wish to measure and then point your infrared thermometer at the tape. The tape should have a fairly similar temperature to the surface it’s attached to but the advantage is that the tape has a high emissivity (0.95). | ||||||||||||||||||||||||||||||
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