Image sensors and optical devices

Which infrared wavelength band is mainly detected in thermography, which images the temperature of people and objects?

  1. AAbout 0.4 to 0.7 µm (visible light)
  2. BAbout 8 to 14 µm (long-wave infrared)
  3. CAbout 0.01 µm (extreme ultraviolet)
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Answer: B. About 8 to 14 µm (long-wave infrared)

Thermal radiation from objects near room temperature is strongest around 10 µm, and this band is also an atmospheric window with little absorption, so thermography detects long-wave infrared at about 8 to 14 µm. Silicon does not absorb light at these wavelengths, so sensors based on other principles, such as microbolometers, are used.

  • A. Visible light is not used to measure object temperature.
  • B. Correct. The 8–14 µm band, where room-temperature thermal radiation is strong, is used.
  • C. Extreme ultraviolet is the wavelength used for EUV lithography.
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