E = hf = hc/λ. The Planck equation and its equivalent.
The Plank's equation is not only applicable to photons, but as we know, it's applicable to all forms of waves, as long as there is measurable frequency of a wave or oscillation, it's applicable.
The Planck's equation adequately gives us a better picture of the universe that the existence in the Universe fundamentally consisting of vibrations and, as vibrational energy dissipates in transmission due to spatial expansions, gravitational redshift etc. its energy and so its frequency get reduced and so converted in other forms.
E.g. a light signal converts into infrared, then microwave, even into radio waves. All these are the result of dissipation of wave energy.
The Planck's equation so conveys us.
Planck's constant h = 6.625 × 10–34 Js