The quantization of energy refers to the absorption or emission of energy in discreet packets, or quanta. As the intensity of electromagnetic energy increases or decreases, it steps up or down from one quantized level to another, rather than follow a smooth and continuous curve. The quantization of energy, also known as "quantum theory," describes how energy can only be lost or gained in multiples of a smallest possible unit of energy, which is referred to as a "quantum."
The quantum hypothesis was first introduced by the German physicist, Max Planck, in 1900. His theory was presented as a means of explaining why the changing levels of energy emitted from the surface of a heated body did not follow a smooth curve relative to the degree of that body's temperature change. This could not be explained by the classical laws of physics. Planck developed a mathematical model which described the quantized change in energy emission or absorption that was based on a constant now known as the "Planck constant."
In 1905, Albert Einstein used Planck's constant to develop the formula, "E = hf," to determine the quantized energy level of a photon traveling in a beam of light. In Einstein's formula, "E" represents the energy contained in a single photon, "h" is Planck's constant and "f" is the photon's frequency.
When Planck first introduced quantum theory in 1900, he did not realize that it would lead to a fundamental change in the way that energy and the physical world were understood by science. The application of Planck's constant also led to the development of the integrated circuits and transistors that play a significant role in modern technology.