Answer
The classical expression agree with the Planck expression in the longer wavelength range.
Work Step by Step
We have already calculated that
$\frac{I_c}{I_p}\approx 3.7\times 10^{6}$ (for a wavelength of $400$ $nm$),
or, $I_c\gt\gt I_p$
and $\frac{I_c}{I_p}\approx 1.017$ (for a wavelength of $200$ $\mu m$),
or, $I_c\approx I_p$
Therefore, we can say that the classical expression agree with the Planck expression in the longer wavelength range.
