In his 1900 analysis of black-body radiation, Max Planck proposed that energy is emitted and absorbed in discrete packets.
A black body is an idealized object that absorbs and emits radiation across wavelengths. Classical physics predicted an incorrect high-frequency result known as the ultraviolet catastrophe. Planck matched the observed spectrum by assuming that oscillators in the material could exchange energy only in amounts proportional to frequency.
He expressed the relationship as E = hν, where E is the energy of a packet, ν is frequency, and h is Planck’s constant. Planck initially viewed the quantization as a mathematical device, but it became a foundation of quantum theory.
The later explanation of the photoelectric effect by Albert Einstein gave the quantum idea a physical interpretation involving light quanta. Planck’s work concerned the black-body spectrum, not a single mechanical laboratory apparatus.