Understanding Emissivity (Infrared Thermometers)
Summary: Emissivity is a measure (rated 0 to 1) of a material's ability to emit thermal energy. Most organic materials (food, skin, wood) have a high emissivity (~0.95), which is the default setting for most infrared thermometers. Shiny metals have low emissivity and reflect ambient room temperature, leading to inaccurate readings unless the thermometer is adjusted.
The "Shiny Metal" Problem
Infrared thermometers work by reading the heat energy radiating off a surface.
- High Emissivity (Easy): Materials like food, cardboard, and dark pans emit their own heat efficiently. The thermometer reads them easily.
- Low Emissivity (Difficult): Polished metals (stainless steel, copper, aluminum) act like mirrors. They do not emit much heat; instead, they reflect the heat of the room.
Example: If you point an IR gun at a shiny stainless-steel pot of boiling water (212°F), the reading might show only 100°F. This is because the metal is reflecting the cool room temperature rather than emitting the heat of the water.
Common Emissivity Values
If your infrared thermometer has Adjustable Emissivity (like the IR-PRO or Industrial Gun), use these general settings:
| Material Type | Typical Emissivity | Device Setting |
|---|---|---|
|
Organic Materials (Food, Water, Skin, Plastic, Wood) |
0.95 - 0.97 | 0.95 (Default) |
|
Oxidized Metal (Cast Iron, Rusted Steel) |
0.70 - 0.90 | Adjust to match Table |
|
Polished Metal (Stainless Steel, Aluminum, Copper) |
0.10 | Adjust to match Table |
How to Measure Low-Emissivity Surfaces
If you must measure a shiny metal surface (like a griddle or pan), you cannot change the physics of the metal, but you can change the surface.
- The Oil Method: Spray a thin patch of cooking oil on the pan. Oil has an emissivity of ~0.95. Measure the oil patch, not the dry metal.
- The Tape Method: Place a piece of masking tape or electrical tape on the surface. Allow it to heat up, then measure the tape. Tape has an emissivity of ~0.95.
- The Matte Black Method: Paint a spot with high-temp matte black paint.
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