In infrared astronomy, the K band is an atmospheric transmission window centered on 2.2 üm (in the near-infrared 136 THz range). HgCdTe-based detectors are typically preferred for observing in this band.
Photometric systems used in astronomy are sets of filters or detectors that have well-defined windows of absorption, based around a central peak detection frequency and where the edges of the detection window are typically reported where sensitivity drops below 50% of peak. Various organizations have defined systems with various peak frequencies and cutoffs in the K band, including , and K<sub>S</sub>, and K<sub>dark</sub>.