What you need to know about emissivity and infrared energy

Thermal imaging

Using a Fluke infrared camera, it's important to understand the relevance of emissivity to temperature measurement calculation.


All objects radiate infrared energy. The quantity of energy radiated is based on the actual surface temperature and the surface emissivity of the object. The imager senses the infrared energy from the surface of the object and uses this data to calculate and estimate temperature value. Many common objects and materials such as painted metal wood, water, skin and cloth are very good at radiating energy and it's easy to get relatively accurate measurements.

For surfaces that are good at radiating energy or highly emissive, the emissivity factor is greater than 0.9 or 90%. Based on zero to one or zero to 100%. This simplification does not work well in shiny surfaces such as the one that we're about to see.

Unpainted metals, as they have an emissivity of less than 0.6 or 60%. These materials are not good for radiating energy and are classified as low emissivity.

Let's take a look at the frying pan we have in front of us. Now the burner is heated up, I've been running some water around here just for effect, get rid of the water.

Now, what's what I want to do is let's go ahead and accurately measure.

Let's focus in, measure. We see we're about 500, now 480, 490 degrees here Fahrenheit. As I flip the pan over, you see that oh, it's only a hundred degrees Fahrenheit.

The difference here is the emissivity value is much lower on the shiny metal surface than it is on the more highly emissive surface of the inside of the pan. The Teflon gives you some added emissivity versus the shiny metal, giving us a very different temperature. But, both being set on the same area for a length of time and knowing that they should be equal.

Now you can mitigate this by using tape or paint on these shiny surfaces. Collect information from those areas to get a more accurate reading...

Featured resources