The energy density for wavelength in range 1-1.1 mm is = 3.44e-11 J/m^3.
The energy density for wavelength in range 100-101 mm is = 1.27e-60 J/m^3.
Thus for shorter wavelengths the energy densities predicted by Rayleigh-Jeans law and Planks law are considerably different while for longer wavelengths the energy densites predicted are same.s