What far infrared is: wavelength and how heat travels

JPHEAT editors (Kawaguchi Seiken Co., Ltd.) / Updated 15 Nov 2026

Light with a long wavelength.

Light is named by its wavelength. Light with a longer wavelength than visible light is infrared, and it cannot be seen. The CIE defines infrared as roughly 780 nm (0.78 μm) to 1 mm. [1]

The bands depend on the standard.

The CIE divides infrared into IR-A (0.78–1.4 μm), IR-B (1.4–3 μm) and IR-C (3 μm–1 mm). [1]

The boundaries of near, mid and far infrared, however, differ by field and use. The BOKEN Quality Evaluation Institute, a Japanese textile testing body, describes 3–1,000 μm as far infrared. [3] When you see the terms, check which standard they follow.

Everything with a temperature gives off infrared.

Objects give off infrared according to their temperature. The hotter they are, the shorter the peak wavelength; the cooler, the longer (Wien’s displacement law). For objects near room or body temperature the peak lies at about 9–10 μm, in the far-infrared range.

Infrared thermometers and thermal cameras capture this infrared and convert it to a surface temperature. [10]

Heat travels three ways.

Heat travels by conduction between things in contact, by convection through moving air or water, and by radiative transfer as infrared and other light, without passing through the air. [2]

The warm surface of a heater, a floor or a mat also gives off infrared. Products used in contact with the body or the floor pass heat by conduction as well.

Absorbed, it becomes heat.

When infrared is absorbed, it turns into heat. The International Commission on Non-Ionizing Radiation Protection explains that long-wavelength infrared (IR-C) is absorbed in the layers near the surface. [5] This is a general physical explanation and says nothing about how any product acts on the human body.

Far infrared in daily life and industry.

Far infrared is nothing unusual. It is widely used for heating, such as floor heating and far-infrared heaters, for removing moisture from coatings and food, and in charcoal grills and ovens. [6][7][8][9] Infrared thermometers and thermal cameras, the infrared images of the Himawari weather satellites (the 10.4 μm band and others) and the AKARI infrared astronomy satellite (50–180 μm) all capture infrared. [10][11][12]

What can and cannot be said.

What can be said with certainty about far infrared are physical facts: how it is classified by wavelength, that it carries heat without passing through the air, and that it turns into heat when absorbed.

The wavelength bands say nothing about how it acts on the human body. Near field is a different idea, about distances between objects, and does not mean near infrared. [4] Nor can a wavelength figure alone tell you how warm something feels: that depends on temperature, the amount given off, contact and the conditions of use.

About JPHEAT’s measured data.

JPHEAT had a third-party testing body measure the relative emission spectrum and the normal total emissivity of a test sample of the JPT100J single underblanket. Among the recorded points, the relative intensity peaked at about 8.35 μm (in the CIE IR-C band), and the normal total emissivity was 0.89.

Both are results for the JPT100J test sample under the test conditions. They are not values for other models or for every setting, and they do not measure any action on the human body.

Questions and answers

What is far infrared?

The name for the long-wavelength part of infrared, which cannot be seen. In the CIE bands it corresponds roughly to IR-C (3 μm–1 mm), and BOKEN describes 3–1,000 μm as far infrared. The boundaries differ by field and use.

How do near, mid and far infrared differ?

They are classified by wavelength, but the boundaries differ by field and use. The CIE uses the bands IR-A, IR-B and IR-C. When you see near, mid and far, check which standard defines them.

Does far infrared glow red?

No. Far infrared cannot be seen. Heaters that glow red are giving off visible light as well as infrared.

How does far infrared carry heat?

By radiative transfer, which needs no moving air, and it turns into heat when absorbed. Heat also travels by conduction and convection.

Are near field and near infrared the same?

No. Near infrared is the name of a wavelength range; near field is an idea about distances between objects. Studies of radiative heat transfer use it for what happens across very small gaps.

Does the wavelength tell you how warm it is?

A wavelength figure alone cannot tell you how warm something feels. Temperature, the amount given off, contact and the conditions of use all play a part.

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What far infrared is: wavelength and how heat travels.