What is Emissivity?

Emissivity is the relative ability of a surface to emit energy by radiation and varies in value between 0 and 1.

In general, the duller and blacker the surface, the closer its emissivity is to 1.

Why Does Emissivity Matter to Me?

Different surfaces have different emissivity values, and these values impact the instruments we use to take temperatures. If the emissivity value is not set correctly on infrared thermometers for the surface being measured, then they will display incorrect temperatures.

What Do I Need to Do About It?

If you take a temperature that seems high while using an infrared thermometer, check the emissivity setting on the thermometer as shown in the figure below. The value should be set to 0.95 for most normal rounds.

To adjust emissivity, repeatedly press the MODE button while the display is on HOLD until the emissivity symbol blinks. Then use the arrow keys to set the value to 0.95.

What Are Typical Emissivities?

Typical values for selected surfaces are:

Clean Snow: 0.83

Soil: 0.92 to 0.96

Brick: 0.93 to 0.96

Black rubber: 0.94

Powdered Charcoal: 0.96

Human Skin: 0.98

How Do I Measure a Shiny Surface?

If you must use an infrared thermometer to measure the temperature of a low-emissivity surface (such as clean copper piping or a stainless tank), cover the surface with a flat black paint beforehand. Raising the emissivity of the surface in this manner is generally easier than precisely measuring the original emissivity.

However, the best tool for low-emissivity surfaces is a contact probe.