When light is absorbed by matter, it can transfer energy to the matter and cause its temperature to increase, resulting in the generation of heat. This process occurs due to the interaction between photons (particles of light) and the atoms or molecules within the material.
When a photon is absorbed, it transfers its energy to the absorbing material. This energy is then converted into thermal energy, increasing the internal kinetic energy of the atoms or molecules. The increased kinetic energy leads to an increase in the random motion of the particles, which we perceive as an increase in temperature or the generation of heat.
On the other hand, matter does not typically emit light spontaneously at ordinary temperatures (excluding incandescent objects or high-temperature sources). Heat, which is thermal energy, can be transferred from matter to other matter or the surroundings by means of conduction, convection, or radiation. However, the heat transfer does not result in the emission of light in the absence of other specific mechanisms.
The emission of light typically requires the excitation of electrons in atoms or molecules to higher energy levels, followed by their subsequent relaxation back to lower energy levels, releasing photons in the process. This process of light emission is distinct from the absorption of light.
In summary, light can give off heat when absorbed by matter because the energy of the absorbed photons is converted into thermal energy, increasing the temperature of the material. However, the reverse process, where matter spontaneously emits light when heated, requires specific conditions and mechanisms related to the excitation and relaxation of electrons in atoms or molecules.