# Do all solid objects emit visible light?

Are there solid objects that do not emit visible light?

To my limited and humble knowledge, creating such an object would require us to "only" shift the spectrum of emitted radiation. Is it possible? If yes, how?

• Cold objects usually do not emit visible light... – CuriousOne May 5 '16 at 6:03
• Do you mean reflect visible light? All materials emit EM radiation due to black body emission, but at normal temperatures the amount of visible light emitted is negligibly small. – John Rennie May 5 '16 at 6:07
• Good catch. Haven't thought it through really. Those stupid morning thoughts.. :) Thank you all for your response. – sjaustirni May 5 '16 at 18:03
• Do perfectly reflecting bodies radiate? – Keith McClary May 6 '16 at 5:14

The microscopic mechanism of emitting photon in a solid is the transformation of kinetic energy of atoms into EM energy. If an atom is in an excited state due to collisions among other atoms, then it will emit photon when it jumps into the ground state, and the energy of the photon is $$E=\varepsilon(\text{excited state})-\varepsilon(\text{ground state})\sim k_{B}T$$
The energy of the photon of visible light is about $2\sim3\,\mathrm{eV}$. So if the temperature $k_{B}T\ll2\,\mathrm{eV}$, then the solid is difficult to emit visible light. The normal indoor temperature is $298\,\mathrm{K}$, i.e. $k_{B}T\sim0.025\,\mathrm{eV}$, so it is difficult to emit visible light in a solid in normal indoor temperature.