I was always under the impression that thermal radiation is essentially infrared energy, so what's the difference between a full thermal imaging camera (e.g. an FLIR) and a standard infrared CCD chip? Surely the latter should function as the former? Yet the price difference is astronomical.

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    \$\begingroup\$ rawbrawb is correct. An infrared CCD detects "thermal" infrared from objects that are about the temperature of the sun. A FLIR detects infrared from objects that are about the temperature of the human body. The wavelength of these IR emissions is very different. Trying to detect emissions from body temperature objects is much harder when your lenses and detector are near the same temperature. \$\endgroup\$
    – Joe Hass
    Sep 2, 2013 at 2:43

1 Answer 1


CCD's are made from Si which has a bandgap of 1.12 eV. This means that it can sense a limited amount of thermal radiation at about ~ 1 um wavelength or shorter. This is called Near IR or NIR. Thermal sensors in the meantime, sense thermally emitted radiation ~ 10 - 14 um wavelength (this is the radiation emitted by a warm body at ~ 300 kelvin). The photons associated with a thermal IR scene are 10X as long and therefore 1/10 th the energy of a NIR photon (1 um vs. 10 um). For a direct bandgap detector, Like MCT (Mercury Cadmium Telluride) these must be cryogenically cooled (77 Kelvin) or the detector will get swamped by it's own heat. There are bolometer based sensors that are less sensitive. But a FLIR is specifically a MCT detector. MCT as a detecting material is very expensive with low yields.

  • \$\begingroup\$ I'm not sure I follow - are you telling me that thermal cameras contain cooling mechanisms that bring the sensor down to -196°C? That seems implausible considering that battery powered hand-held devices exist and don't get excessively hot. \$\endgroup\$
    – Polynomial
    Sep 1, 2013 at 23:09
  • \$\begingroup\$ An FLIR is a MCT device and must be cooled. A handheld device is a micro-bolometer with lower performance. You are conflating IR with Thermal IR (from general to specific) and FLIR with Thermal sensor (from specific to general) . Which is understandable because the company that has the largest market share is also called FLIR ... \$\endgroup\$ Sep 1, 2013 at 23:28
  • \$\begingroup\$ FLIR makes many kinds of sensors, including bolometer arrays that are extensively used in portable equipment. I've recently been working on one system that uses a 640x512 pixel microbolometer array. It's temperature-stabilized, but not chilled. \$\endgroup\$
    – Dave Tweed
    Sep 1, 2013 at 23:29
  • \$\begingroup\$ To top it off, different industries use different definitions for the regions of IR. Astronomy and spectrographic use Mid- IR, the Military uses thermal IR (TIR) for the same 10 -14 um band. IR in general spans a huge band of energies though. \$\endgroup\$ Sep 1, 2013 at 23:30
  • \$\begingroup\$ And FLIR started with FLIR's but now also use uBolometers. \$\endgroup\$ Sep 1, 2013 at 23:31

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