Planck Postulate
Planck 
postulated that the energy of oscillators in a
blackbody is quantized by

(1)
where
n = 1, 2, 3, ...,
h is
Planck's constant, and

is the frequency, and used this postulate in his derivation of the
Planck law of blackbody radiation. In fact, electromagnetic radiation is itself quantized, coming in packets known as
photons and having energy

(2)
In the other hand, the energy of state
n of quantum mechanical
simple harmonic oscillator is actually given by the slightly modified form

(3)