The Boltzmann constant sets up a relationship between wavelength and temperature (dividing hc / k by a wavelength gives a temperature) with one micrometer being related to 14 387.777 K, and also a relationship between voltage and temperature (kT in units of eV corresponds to a voltage) with one volt being related to 11 604.518 K. The ratio of these two temperatures, 14 387.777 K / 11 604.518 K ≈ 1.239842, is the numerical value of hc in units of eV⋅μm.