When measuring temperature with an infrared camera, what is the most reliable source for the emissivity value?

• A. The Source Being Measured
• B. The Manufacturer's Default Values
• C. A Standard Reference Table
• D. An Estimated Value

Answer: (A)

Emissivity is the property of a surface that determines how efficiently it emits infrared radiation at a given wavelength. Since the infrared camera converts detected radiance into temperature using this emissivity value, the most reliable source is the actual surface you’re measuring. The true emissivity depends on the material, its finish, coatings, roughness, oxidation, and even the viewing angle and temperature. All of these can differ from surface to surface and change over time, so the emissivity of the exact spot you measure is the value that will give you the correct temperature reading.

Using a standard reference table or manufacturer defaults can be helpful as a starting point, but they’re approximations and may not match your specific surface conditions. An estimated value is the least reliable because it lacks validation against the real surface. If possible, calibrate or determine emissivity directly on or very near the area of interest, or use a known reference target with a validated emissivity to set the camera. This approach minimizes errors and yields more accurate temperature measurements.