How to Measure Temperature With Infrared

How to Measure Temperature With Infrared. Infrared, or IR, temperature measurement is important in industry as it allows non-contact temperature measurement of still or moving objects from a distance. Infrared energy is the invisible light emitted by all substances with a temperature greater than absolute zero, 0-degrees Kelvin, which is equal to minus 459.67 degrees Fahrenheit. Its wavelength shift with temperature changes underlies its use for temperature measurement. Differences in the way various substances emit IR energy and surrounding conditions complicate the IR temperature measurement process. Infrared measurements of temperature therefore improve as these issues are alleviated.

A small handheld infrared temperature "gun" aims a laser dot to help point to the right place to measure temperature.

Things Needed

  • Infrared Thermometer Device (IR Temperature Gun)

Step 1

Identify the temperature target. Most uses of infrared thermometers, or IRTs, focus on specific products, as opposed to measuring random surfaces out of curiosity. A brick manufacturer may aim the IRT at bricks emerging from an oven. A food manufacturer uses an IRT to sense the temperature of cold red meat without contacting it. Materials exhibit different emissivity values. Because emissivity data for most common substances is widely published, the IRT application can be compensated for best accuracy.

Step 2

Correct the field of "view." IRT optics focus on a zone on the object being measured. Each instrument has its own focal information. The zone should be at most one half the size of the object measured. For a 3-inch brick, a focal zone less than 1 1/2 inches in diameter is fine. If the focal spot zone is greater than one half, move the IRT proportionately closer to the object. So if the focal zone diameter is equal to the size of the object, and it is 4 feet away from it, move it to within 2 feet to halve the focal area diameter.

Step 3

Consider surroundings. If the IRT is used in a food cooking plant to measure cooked products, its temperature readings may be affected by steam or fumes. Steam may condense on the lens of a fixed IRT suspended above a hot conveyor belt. For this reason, many IRT applications blow very dry air at ambient temperature over the lens to keep it dry and clear. The user may have to install a dust collection system around a milling area or a fume extractor near a smoky heating operation.

Step 4

Compensate for sudden ambient temperature changes in the area where the IRT will be used. Sudden changes in ambient temperature can drastically affect the performance of an IRT, due to aspects of its electronics that compensate for this variable. Sudden changes can "trick" an IRT into outputting a false value before the compensation circuitry has time to catch up. For this reason, IRT sensors are available with water or air-cooling options.

Step 5

Validate the IRT application with a contact-type temperature sensor. Experienced IRT users calibrate their systems by actually measuring the object's temperature with a regular temperature probe, and fine-tweaking the non-contact IRT output to match that value.

Step 6

Maintain precise consistency when using the IRT from day to day. Measuring a new material, moving the sensor around or changing the surrounding conditions can alter IRT performance significantly. Review the application regularly to make sure your approach to using it is consistent.


  • Use IRT guns to measure unknown temperatures prior to touching unknown objects.
  • Some IRT devices have a red laser pointer to help aim the IRT focal point.


  • The temperature readings from spurious and arbitrary use of infrared temperature guns can vary significantly from true temperature.


  • Omega Engineering: Infrared Temperature Measurement Theory and Application
  • Raytek/Division of Fluke Company: Emissivity (IR)
  • Thermoworks: Emissivity Table (Common Materials)