My chef friend insists on using a laser thermometer to measure the temperature of anything he cooks. How can it read the temperature without touching the surface of the food?

Laser thermometers work on the same principle as infrared (IR) thermometers; the laser is just there so that you can see what you’re aiming at. IR thermometers are often used in industrial manufacturing to measure the temperature of very hot things or inaccessible areas, or in food manufacturing to make sure that frozen foods are cold enough or hot foods are hot enough. Those body-temperature thermometers you stick in your ear also operate using the same technology.

IR thermometers take advantage of the fact that all molecules in matter are constantly vibrating: The higher their temperature, the faster the vibrations. When you point an IR thermometer at an object, a series of mirrors and lenses inside detects those vibrations in the form of infrared radiation—energy at a longer wavelength than visible light. By analyzing the wavelength of the infrared, the thermometer figures out how fast the molecules are vibrating, and thus their temperature. IR thermometers work best on dark, dull-colored objects—shiny things can reflect infrared energy from other sources in addition to giving it off themselves, which can interfere with the reading.

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