In physics, the Draper point is the approximate temperature above which almost all solid materials visibly glow as a result of black-body radiation.
[1][2][3] Bodies at temperatures just below the Draper point radiate primarily in the infrared range and emit negligible visible light.
where Substituting the Draper point into this equation produces a frequency of 83 THz, or a wavelength of 3.6 μm, which is well into the infrared and completely invisible to the human eye.
However, the leading edge of the blackbody radiation curve extends, at a small fraction of peak intensity, to the near-infrared and far-red (approximately the range 0.7–1 μm), which are weakly visible as a dull red.
[5] According to the Stefan–Boltzmann law, a black body at the Draper point emits 23 kW of radiation per square meter, almost exclusively infrared.