In this situation, Kirchhoff's law of equality of radiative emissivity and absorptivity and the Helmholtz reciprocity principle are in play.
equilibrium | Thermodynamic equilibrium | Mechanical equilibrium | Thermal insulation | thermal conductivity | Solar thermal energy | Paleocene–Eocene Thermal Maximum | Nuclear thermal rocket | general equilibrium theory | Farakka Super Thermal Power Station | Dynamic stochastic general equilibrium | Chemical equilibrium | chemical equilibrium | Yatağan Thermal Power Plant | Thermal transfer | Thermal shock | Thermal Probe Lithography | Thermal printing | thermal insulation | thermal energy storage | Thermal Emission Spectrometer (TES) | Thermal Emission Spectrometer | Thermal cycler | Thermal conductivity | Solar thermal rocket | Punctuated equilibrium | Ocean thermal energy conversion | Nash equilibrium | List of types of equilibrium | Kirchhoff's law of thermal radiation |
Maxwell–Boltzmann statistics, statistical distribution of material particles over various energy states in thermal equilibrium
M. Zemansky also distinguishes mechanical, chemical, and thermal equilibrium.