this post was submitted on 27 May 2026
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hmmm
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For things that are "hmmm".
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My understanding is that it doesn't really depend on the metal much. It's just the blackbody radiation associated with that temperature. So basically anything glowing red from heat is probably over 500°C.
"As the object increases in temperature to about 500 °C (773 K; 932 °F), the emission spectrum gets stronger and extends into the human visual range, and the object appears dull red."
https://en.wikipedia.org/wiki/Black-body_radiation
The intensity does depend on the emissivity of the material, and emissivity is a bit counterintuitive:
https://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html
But less than you’d think, given the extreme coefficient, as human perception of brightness is nonlinear. An object twice as bright as another looks pretty similar to the eye.
Thanks for the correction. I'm absolutely not gonna pretend I fully understand this, but isn't it still the case that anything glowing red from heat pretty much has to be over 500°C? I.e. https://en.wikipedia.org/wiki/Draper_point ?
Oh yeah, for sure. That pipe is hot.
Thanks!