# A Incandescence and electronic excitation

1. May 23, 2016

### hokhani

As far as I experienced, incandescence happens in a wide variety of materials no matter what a substance (conductor, insulator and so on) is. Does this effect is related to the electronic excitation? Could anyone please explain the reason of this effect?

2. May 23, 2016

### Staff: Mentor

At equilibrium, the thermal energy is spread out into all degrees of freedom that are not "frozen" (i.e., for which there is enough energy to lead to a significant population of the excited states). For high enough T, that includes electronics degrees of freedom. In the solid state, electronic states usually constitute continua, such that emission is over a wide range of the electromagnetic spectrum.

You should look up blackbody radiation.

3. May 23, 2016

### hokhani

In an ideal insulator electrons can not pass the large gap by thermal energy and so there is no electron excitation. How does an insulator show this effect?

4. May 24, 2016

### Staff: Mentor

States are populated with a probability proportional to $e^{-E/kT}$. There is always some thermal electronic excitation, even though it can be neglected in most cases. But there is always a point where the temperature is high enough that it is not negligible anymore, and the object will glow.