The concept of quantum theory radiation is attributed to Max Planck. In 1900, Planck was trying to explain the observed spectrum of blackbody radiation, which is the radiation emitted by a heated object. Classical physics at the time could not account for the observed spectrum, particularly the fact that it peaked at a specific wavelength depending on the temperature.

Planck proposed that energy was not emitted or absorbed continuously, but in discrete packets called quanta. He suggested that the energy of each quantum was proportional to the frequency of the radiation, with the proportionality constant being a new fundamental constant called Planck's constant (h).

This revolutionary idea marked the birth of quantum mechanics and revolutionized our understanding of light and matter. While Planck initially introduced the concept to explain blackbody radiation, it later became the cornerstone for explaining various other quantum phenomena, including the photoelectric effect, the wave-particle duality of light, and the Bohr model of the atom.