This concept is inferred from quantum mechanics. According to quantum mechanics, electrons can absorb or emit energy by a discrete amount of energy called quanta. This follows from the two contradicting theory of wave-particle theory of light. It was widely accepted already that light behaves like a wave. However, questions are still unanswered on why electromagnetic waves emit or absorb light in specific frequencies. Until Planck proposed his equation: E = hν, where E is the energy, h is called the Planck's constant and ν is the frequency.
In this equation, it signifies that increase energy is progressing at discrete amounts of frequencies and this constant is denoted by h.
