- Draper point
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.
Bodies at temperatures just below the Draper point radiate primarily in the infrared band and at longer wavelengths, and emit negligible visible light. The value of the Draper point can be calculated using Wien's displacement law: the peak frequency νpeak (in hertz) emitted by a blackbody relates to temperature as follows:
- k is Boltzmann's constant.
- h is Planck's constant.
- T is temperature (in kelvins).
Substituting the Draper point into this equation produces a frequency of 46.9 terahertz—which is infrared, and largely invisible except for a dull red, at a small fraction of the peak intensity, that is visible to the human eye.
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