Draper point explained

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

\nu _{peak} (in hertz) emitted by a blackbody relates to temperature as follows:^[4] $$\backslash nu\_\backslash text\; =\; 2.821\; \backslash frac,$$where

• is the Boltzmann constant,
• is the Planck constant,
• is temperature (in kelvins).

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 metre, almost exclusively infrared.

See also

• Incandescence

Notes and References

1. On the Production of Light by Heat . John William . Draper . The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science . 30 . 1847 . 202 . 345 - 359 . Series 3 . 10.1080/14786444708647190 .
2. The Academy . Science: Draper's Memoirs . 14 . 338 . John William . Draper . Robert Scott Walker . London . Oct 26, 1878 . 408 .
3. Book: Mahan , J. Robert . Radiation heat transfer: a statistical approach . 3rd . Wiley-IEEE . 2002 . 978-0-471-21270-6 . 58 .
4. Book: Wannier, Gregory H. . Statistical Physics . Gregory Wannier . 1987 . 1966 . . . 978-0-486-65401-0 . 15520414 . Chapter 10-2 .
5. Book: Starr, Cecie . Biology: Concepts and Applications . Thomson Brooks/Cole . 2005 . 0-534-46226-X .