Questions and answers related to th IR emissivity of surfaces. Most likely related to IR temperature measurement, or thermal equilibrium.
All materials above absolute zero radiate IR energy to their environment. Every object also absorbs IR energy from their environment.
The rate of energy radiation per unit area is proportional to the fourth power of the absolute temperature.
The rate of radiation and absorption is also proportional to a property called "emissivity".
A perfect "black body" has an emissivity of 1. A perfect reflector has an emissivity of 0. Practical material are somewhere in between, with soot blacken metal surface around 0.98, and a highly polished metal surface down to less than 0.1.
The emissivity is relevant when considering thermal equilibria, and also when using IR thermometers. In the latter case, highly reflective material will appear colder than they actually are, unless the IR detector is calibrated with the actual emissivity.
