What helps when trying to measure the temperature of a low emissivity object with an infrared camera or non-contact thermometer?

• A. Changing the emissivity setting
• B. Using a longer lens
• C. Increasing distance
• D. Calibrating to ambient temperature

Answer: (A)

Emissivity is the property that determines how much infrared energy a surface actually emits versus how much it reflects from the surroundings. When a surface has low emissivity, it emits less radiation and reflects more ambient infrared energy. An infrared camera or non-contact thermometer relies on a assumed emissivity to convert the measured radiance into a temperature. If you adjust the device’s emissivity setting to match the real surface, you’re telling the instrument how much of the detected energy is emitted by the object, not just reflected, which makes the temperature reading much more accurate for that surface.

Other adjustments don’t fix this fundamental issue. A longer lens changes the field of view and resolution, not the amount of energy the surface emits. Increasing distance widens the spot and can reduce measurement accuracy, again not addressing emissivity. Calibrating to ambient temperature can help account for reflected ambient radiation in some cases, but it doesn’t replace the need to set the correct emissivity for the surface to obtain a true surface temperature.