How Does an Infrared Thermometer Work?

How Does an Infrared Thermometer Work?

There are different temperature measurement devices used in industrial and clinical environments. The most commonly used is a thermometer at clinics. However, the use of Infrared thermometers has recently increased because of their more practical work. It can detect object temperature without touching it, which helps to avoid viral disease transmission.

You must think about how an infrared thermometer works to measure the temperature. An infrared Thermometer uses thermal radiation to detect the temperature without making physical contact. Let’s take a detailed look at how an infrared thermometer works.

What do Infrared Thermometers Do?

Infrared Thermometers do temperature measurements of the object, detecting the intensity of infrared radiations. It is an alternative temperature measurement source when other devices don’t work practically, particularly when the thing is fragile or dangerous to get near.

Because it can detect the object’s temperature from a distance, making it useful and safe in such conditions. It doesn’t need to sterilize before use and reduces the risk of viral disease transmission among people.

How Does Infrared Thermometer Work?

An infrared thermometer works on infrared radiations. So, the working principle is simple and discussed below in detail.

Infrared Radiations

The objects emit infrared radiations produced by the movement of molecules because no entity couldn’t have absolute zero temperature. The atom’s movement produces heat and energy, which correlate with the object’s temperature. The increased motion of molecules means more IR rays.

Infrared radiation is electromagnetic radiation that lies just outside the visible light spectrum. It has a longer wavelength than visible light and is not visible to the naked eye. However, we can feel it as heat.

Hitting these radiations on metals can produce heat which can help to measure the body temperature. So, we can focus the radiations on the thermometer lens, which funnels them to the detector.

Measurement of Intensity of Infrared Radiations

An infrared thermometer consists of a lens to focus the infrared radiation, a sensor to measure the radiation, and a processor to analyze the data and display the temperature reading.

The lens of the infrared thermometer focuses the radiation onto the detector, which is called a thermopile or a pyroelectric sensor. These detectors are sensitive to temperature changes and convert infrared radiation into an electrical current.

The processor then analyzes the electrical current and calculates the temperature of the object based on the amount of infrared radiation it is emitting. This calculation is based on the principle of blackbody radiation, which states that the amount of radiation emitted by an object is directly proportional to its temperature.

So, infrared radiation’s intensity can be measured using the lens, detector, and data analyzer in an infrared thermometer. Higher IR rays intensity means higher voltage production, which means higher temperature value and vice versa.

The whole working process of an infrared thermometer seems complicated. Still, it takes just seconds to measure the temperature, which makes an infrared thermometer ideal to use at different places such as airports, industries, food stores, and clinical locations.

What Can Affects the Working of an Infrared Thermometer?

An infrared Thermometer is an excellent tool for measuring the temperature easily and accurately. But there are a few limitations that can affect the reading of the thermometer, and you can get wrong results. Below we are discussing all these limitations.

Distance, Angle, and Surrounding

Distance: Each thermometer comes with different ranges of distance from the object to measure the temperature, called the distance-to-spot ratio. The most common ratio of thermometers available in the market is 4:1, 8:1, 30:1, and 50:1.

The thermometer with an 8:1 ratio can take accurate measurements by standing 8 inches from the target at an area of 1 square inch. Otherwise, you will end up getting incorrect results. Because the infrared energy emitted by the object will weaken as the distance increases, leading to a less accurate measurement.

Angle: The angle at which the infrared thermometer is pointed at the object also affects the reading. If the angle is too steep, the thermometer may not be able to measure the object’s temperature accurately.

Surrounding: The surrounding environment can also affect the reading of an infrared thermometer. If the thermometer is used in a location with strong sunlight or other heat sources, the reading may need to be more accurate due to interference from these external sources.

Additionally, if other objects surround the object being measured at different temperatures, the reading may be affected by the temperature of these objects.


Emissivity is a measure of an object’s ability to emit thermal radiation. It is defined as the ratio of the radiant energy emitted by an object to the radiant energy emitted by a blackbody at the same temperature. Emissivity is a property of the surface of an object and can range from 0 to 1, with 0 representing a perfect reflector and 1 representing a perfect emitter.

In using an infrared thermometer, an object’s emissivity can affect the temperature reading’s accuracy. Infrared thermometers work by measuring the thermal radiation emitted by an object. The object’s temperature is determined based on the intensity of the radiation and the emissivity of the object’s surface. The temperature reading may be accurate if the object’s emissivity is known or correctly assumed.

For example, if an object has a low emissivity (close to 0), it will reflect a significant portion of the thermal radiation incident on its surface. The infrared thermometer will measure the object’s thermal and thermal radiation reflected off the surface. The resulting temperature reading will be lower than the actual temperature of the object.

On the other hand, if an object has a high emissivity (close to 1), it will absorb and emit a significant portion of the thermal radiation incident on its surface. The resulting temperature reading will be higher than the actual temperature of the object.

To get an accurate temperature reading with an infrared thermometer, it is important to know the emissivity of the measured object and set the infrared thermometer accordingly.

Ambient Temperature

Ambient temperature can affect the reading of an infrared thermometer in several ways. Firstly, the temperature of the surrounding environment can affect the temperature of the infrared thermometer’s sensor, which can lead to inaccurate readings because the sensor’s temperature can change based on the temperature of its surroundings. If the ambient temperature is significantly different from the temperature of the object being measured, it can affect the accuracy of the reading.

Secondly, the air temperature between the thermometer and the measured object can also affect the reading accuracy because the infrared radiation emitted by the object will be absorbed and scattered by the air, which can cause the reading to be inaccurate.

Finally, the ambient temperature can also affect the reflection of the infrared radiation from the measured object. If the object’s temperature is significantly different from the ambient temperature, it can cause the reflection of the infrared radiation to be distorted, leading to an inaccurate reading.

Overall, it is important to ensure that the ambient temperature is consistent and stable when using an infrared thermometer to provide the most accurate readings.


So, how does an Infrared Thermometer work to measure the temperature without getting in touch with the object? The working principle of the infrared thermometer is simple because it detects the IR rays emitted from the object and passes rays from the lens to the detector, producing an electric current in the thermometer; ultimately, the data analyzer gives readings by measuring the electric current.
We also discussed how the working of the infrared thermometer could affect by different external factors such as distance, emissivity, and ambient temperature.