Why 8–15 µm is considered "thermal infrared" if typical room temperature kT is 48 µm?According to Wikipedia:"Long-wavelength infrared (8–15 µm, 20–37 THz, 83–155 meV): The "thermal imaging" region, in which sensors can obtain a completely passive image of objects only slightly higher in temperature than room temperature - for example, the human body - based on thermal emissions only and requiring no illumination such as the sun, moon, or infrared illuminator. This region is also called the "thermal infrared"."However, using h c λ = k B T, the temperature range 288–308 K (15–35 °C) is equivalent to 50–46.7 µm, while 8–15 µm is equivalent to 1800–960 K (using the same equation).

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Why 8–15 µm is considered &quot;thermal infrared&quot; if typical room temperature kT is 48 µm?According to Wikipedia:&quot;Long-wavelength infrared (8–15 µm, 20–37 THz, 83–155 meV): The &quot;thermal imaging&quot; region, in which sensors can obtain a completely passive image of objects only slightly higher in temperature than room temperature - for example, the human body - based on thermal emissions only and requiring no illumination such as the sun, moon, or infrared illuminator. This region is also called the &quot;thermal infrared&quot;.&quot;However, using             h      c        λ    =      k          B        T, the temperature range 288–308 K (15–35 °C) is equivalent to 50–46.7 µm, while 8–15 µm is equivalent to 1800–960 K (using the same equation).

Skyler Barber · Accepted Answer

Your formula is wrong, is the short answer. It works fine as an order of mangnitude approximation, but it&#039;s only an approximation. What you need is Wien&#039;s displacement law:  λ  =      b    T  where Wien&#039;s displacement constant   b  =  2.8977729  (  17  )  ×      10          −      3        m  K. Put   T  =  288  K  ,  308  K into that and you get:  λ  =  9.4  −  10.0  μ  m, which as you&#039;d expect is at the lower range of the thermal infra-red sensors.Note that   b  =            h      c              x              k        B             where   x can be determined from the finding the peak of the black body spectrum from Planck&#039;s law - which has to be done numerically. It turns out that   x  =  4.96, as opposed the value of 1 you in effect used in your original estimate. Hence your values are around a factor of 5 too high.

Why 8–15 µm is considered "thermal infrared" if typical room temperature kT is 48 µm? According to

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