The darker an object is, the more efficiently it absorbs radiation and the hotter it becomes. Conversely, hotter objects emit light of shorter wavelength. Objects with sufficient thermal energy glow visibly red, yellow, white then blue.
Temperature is a measure of the kinetic energy of the atoms of a material. The higher the material temperature is, the more kinetic energy its atoms possess. Light is emitted when charged particles, such as ions or electrons, vibrate. A higher atomic vibrational frequency produces shorter light wavelengths of light. Hotter objects have both a larger number of vibrating charges and higher vibrational frequencies. The spectral distribution emitted from a material depends on its composition. Different elements emit different spectral lines, which combine to produce a continuous emission spectrum.
These compositional differences also lead to differences in the way light is absorbed and re-emitted. Objects that are visibly darker absorb a wider spectral range of visible light. This absorption of light energy raises the kinetic energy of the material atoms, heating the material. Whether a material is transparent, reflective or absorbent to a certain wavelength of incident light depends on its electronic properties, determined by the type of atoms and the way these atoms bond. For example, the lustrous appearance of most metals results from the interaction of the electrons and ion cores in metallic bonds with incident light.