Is a constant obtained by numerically solving the maximum equation; K is Boltzmann constant, H is Planck constant, and T is absolute temperature (in Kelvin). It should be noted that the radiant energy flow density in the above frequency form is defined as "energy radiated through the frequency band with unit area and unit width in unit time", while the radiant energy flow density in the wavelength form is defined as "energy radiated through the wavelength range with unit area and unit width in unit time", so fmax and λmax do not correspond. Therefore, fmax and λmax in wavelength form do not satisfy the relation of frequency × wavelength = wave velocity, that is:
Where c stands for the speed of light.