Hey! Electron diffraction relates to the wave nature of electrons. Light is composed of small packets of electromagnetic particles or photons. So light moves as a wave, and it is proven by the De Broglie wavelength equation. We use it to calculate the wavelength of matter:
λ = h/mv, where λ is wavelength, h is Planck's constant, m is the mass of a particle, moving at a velocity v. Hope that helped!