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Measuring Temperature of Water and Glass through Infrared Thermometers

  • June 30 2023
  • Riho Kato
放射温度計 AD-5635


Can temperatures be measured through water or glass using an infrared thermometer?

Water, being transparent and colorless, might initially seem to have high transmittance

and make temperature measurement impossible.


However, in reality, water has a high emissivity of 0.98,

making it possible to measure surface temperatures using a typical infrared thermometer.

(Reference: What is Emissivity?


However, it's important to note that infrared thermometers are designed to measure surface temperatures,

so they cannot directly measure the internal temperature of water.

However, under the assumption that there is no temperature difference between the surface and the internal region

when the water is gently stirred, it is possible to consider the surface temperature as equivalent to

the internal temperature and indirectly measure the internal temperature.


When measuring temperatures near water, it is recommended to use the water-resistant model AD-5612WP

or the waterproof model AD-5617WP.


Additionally, it is not possible to measure the temperature of an object through glass.

This is because the thermometer will measure the temperature of the glass in front of the object instead.


Radiation thermometers use infrared sensors that are sensitive to the wavelength range of 8 to 14 micrometers

in order to avoid measuring the temperature of the air.

(Reference: Measuring the temperature of air using a radiation thermometer.


Typical quartz glass does not transmit infrared radiation with wavelengths above 5 micrometers.

Therefore, in the wavelength range of 8 to 14 micrometers, which is utilized by radiation thermometers,

glass absorbs and radiates infrared energy well. Consequently, when attempting to measure temperature through glass

using a radiation thermometer, it will measure the temperature of the glass surface instead.

Glass and infrared thermometer


To the human eye, glass appears transparent, and we can see objects through it.

However, in reality, glass has a high emissivity and low transmissivity.

Therefore, on the infrared sensor of a radiation thermometer, glass is considered opaque, and it

is not possible to measure the temperature of an object through glass using a radiation thermometer.