The constant $\textit{Planck Constant}$ is a physical constant that is the quantum of action in quantum mechanics.
The Planck constant was first described as the proportionality constant between the energy ($E$) of a photon
and the frequency ($\nu$) of its associated electromagnetic wave.
http://physics.nist.gov/cuu/Constants/bibliography.html
http://en.wikipedia.org/wiki/Planck_constant
http://dbpedia.org/resource/Planck_constant
$E = h\nu = \frac{hc}{\lambda}$, where $E$ is energy, $\nu$ is frequency, $\lambda$ is wavelength, and $c$ is the speed of light.
http://www.iso.org/iso/catalogue_detail?csnumber=31895