I have an electric stove, and when I turn it on and turn off the lights, I notice the stove glowing.
However, as I turn down the temperature, it eventually goes away completely. Is there a cut-off point for glowing?
What actually is giving off the light? Does the heat itself give off the light, or the metal?
Best Answer
It is due to thermal radiation. Bodies with temperature above absolute zero emits radiation. If frequency of the radiation is in the visual range the body "glows".
This explains that heat itself is not giving off the light.
Spectral energy density as function of of wavelength and temperature
$u(\lambda,T) = \frac{8\pi hc}{\lambda^5} \frac{1}{e^{\frac{hc}{\lambda k T}}-1}$
If you integrate $u(\lambda,T)$ wrt $\lambda$ from $\lambda = 380nm$ to $\lambda = 750nm$ you will find that there is always some radiation in visual range. But it is very very small at room temperature(T = 300K) and hence undetectable to naked eye.
To get cut off temperature($T_c$) for glow. You need to solve
$\displaystyle \int_0^{T_c} \int_{\lambda = 380nm}^{\lambda=780nm} u(\lambda,T)d\lambda dT$ = minimum required to be detected by human eye.