Planck relation in the context of Photon energy

The Planck relation (referred to as Planck's energy–frequency relation, the Planck–Einstein relation, Planck equation, and Planck formula, though the latter might also refer to Planck's law) is a fundamental equation in quantum mechanics which states that the photon energy E is proportional to the photon frequency ν (or f):$${\displaystyle E=h\nu =hf.}$$The constant of proportionality, h, is known as the Planck constant. Several equivalent forms of the relation exist, including in terms of angular frequency ω:$${\displaystyle E=\hbar \omega ,}$$where the reduced Planck constant is ${\displaystyle \hbar =h/2\pi }$.

The relation accounts for the quantized nature of light and plays a key role in understanding phenomena such as the photoelectric effect and black-body radiation (where the related Planck postulate can be used to derive Planck's law).