Draper point

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The Draper point is the approximate temperature above which almost all solid materials visibly glow as a result of blackbody radiation. It was established at 977 °F (525 °C, 798 K) by John William Draper in 1847.[1][2][3]

Bodies at temperatures just below the Draper point radiate primarily in the infrared range and emit negligible visible light; the value of the Draper point can be calculated using Wien's displacement law: the peak frequency (in hertz) emitted by a blackbody relates to temperature as follows:[4]


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 kilowatts of radiation per square metre, almost exclusively infrared.

See also[edit]


  1. ^ Draper, John William (1847). "On the Production of Light by Heat". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. Taylor & Francis: 345–359.
  2. ^ Draper, John William (Oct 26, 1878). "Science: Draper's Memoirs". The Academy. London: Robert Scott Walker. XIV (338): 408.
  3. ^ Mahan, J. Robert (2002). Radiation heat transfer: a statistical approach (3rd ed.). Wiley-IEEE. p. 58. ISBN 978-0-471-21270-6.
  4. ^ Wannier, Gregory H. (1987) [1966]. "Chapter 10-2". Statistical Physics. New York: Dover Publications. ISBN 978-0-486-65401-0. OCLC 15520414.
  5. ^ Starr, Cecie (2005). Biology: Concepts and Applications. Thomson Brooks/Cole. ISBN 0-534-46226-X.