The concept you're looking for is called Emissivity, and it describes how effectively an object can radiate (or absorb!) at a certain wavelength. https://en.wi

The concept you're looking for is called Emissivity, and it describes how effectively an object can radiate (or absorb!) at a certain wavelength. https://en.wikipedia.org/wiki/Emissivity https://en.wikipedia.org/wiki/Emissivity > Real objects never behave as full-ideal black bodies, and instead the emitted radiation at a given frequency is a fraction of what the ideal emission would be. The emissivity of a material specifies how well a real body radiates energy as compared with a black body. This emissivity depends on factors such as temperature, emission angle, and wavelength. However, it is typical in engineering to assume that a surface's spectral emissivity and absorptivity do not depend on wavelength so that the emissivity is a constant. This is known as the gray body assumption. https://en.wikipedia.org/wiki/Black-body_radiation https://en.wikipedia.org/wiki/Black-body_radiation In a previous life I worked for a lab designing a passive radiator that was reflective to visible light but absorptive/emissive in the atmospheric window (where the atmosphere is completely transparent). This material had the fun effect of absorbing energy via conduction/convection and then sending it out into space, maintaining a temperature slightly below ambient.