Is the Drapers point inaccurate? Is the Drapers point faulty since an oven glows visibly red without it actually reaching Drapers point? When the Drapers point blackbody radiation frequency is calculated by Wien's law it results about 82.57 terahertz, while the frequency range of visible light is around 400 THz to 790 THz. So is it faulty?
Wien's law:
$$ \lambda = \frac bT\,.$$
So the $\lambda$ (wavelength) was 3631 nanometers wavelength and its corresponding frequency is 82.57 THz.
 A: Planck's law describes the emission of an ideal blackbody, given in frequency ($\nu$) form as
$$B(\nu,T)=\frac{2h}{c^2}\nu^3n(\nu,T)\;,$$
where $T$ is the temperature and $n(\nu,T)=1/(\exp(h\nu/k_{\rm B}T)-1)$ is the Bose-Einstein distribution.
If you look for the maximum peak ($dB/d\nu=0$), you will find Wien's law:
$\nu=b T$, where $b=0.058$ THz/T. However this is just the peak position, the actual distribution is broad and can reach the visible spectrum even when the peak is outside the visible spectrum, like in Draper's point.
Here is a log-linear graph of the distribution for different temperatures

Note that the peak for all the temperatures shown here is in the infrared and not in the visible, yet at least some have a contribution in the visible.
According to a quick Google search (please verify), the human eye can detect at minimum $10^{-10}$ W/m${}^2$. We can integrate the curves above to obtain the intensity over the visible range, we get:

*

*300 K, integrated intensity (visible): $10^{-19}$ W/m${}^2$.

*798 K (Draper's point); integrated intensity (visible):  $0.064$ W/m${}^2$.

*1000 K, integrated intensity (visible):  $10$ W/m${}^2$.

We can see that at Draper's point, the intensity in the visible is clearly over the human eye threshold. We have to consider that this is not a purely physical matter, it is also a biological question, that's why probably Drapers point is determined empirically. A more precise theoretical calculation is more complicated as it depends on the size of the eye, the human eye response to red, blue, green and so on.
