# Do real materials emit radiation at all wavelengths?

An ideal black body with temperature greater than 0K emits some energy/radiation at all wavelengths. Does a normal body with temperature greater than 0K also emit radiation at all wavelengths?

• Although in theory all wavelengths can be emitted as shown by the spectral radiance formula en.wikipedia.org/wiki/… in practice there is a peak to the emission spectrum and a (fairly rapid) fall off on either side of that peak. Commented Feb 17, 2018 at 11:22
• See this possible duplicate: Why doesn't diamond glow when hot? Commented Feb 17, 2018 at 12:27

## 1 Answer

This is the functional form of the perfect black body radiation's emittance. Notice the logarithmic scale of the emmitance, which means an extremely rapid fall off at the edges of the plots.

Real materials will follow this outline. Here are calculations showing the tails for various temperatures,which are long, for large wavelengths, but still too small to be measurable.

An example of "real material" that follows approximately the theoretical curve is the curve from the sun, which shows deviations from the theory, but no peaks outside the measurable intensities in the spectrum. The peaks and valleys, not good fits, are due to the different concentrations of materials and mechanisms in the heat production of the sun.

The yellow part is what leaves the sun.

The best fit to the black body curve comes from the cosmic microwave background, which has had billions of years to be homogenized.

Do real materials emit radiation at all wavelengths?

It is a matter of probabilities, and how long the observation lasts. The theoretical curve allows very small wavelengths and very long wavelengths. Due to the rapid exponential fall off at the high energy side, it is very improbable for a desk at room temperature to emit a gamma ray. Long wavelengths are more probable, since the curve falls off smoothly at long wavelengths, but again, from sheer numbers, more and more improbable the larger the wavelength.

So it is a conditional yes, with the limits at the long side the dimension of the universe and at the short side the quantum mechanical energies available for creating radiation.

• so... is your answer "yes" or "no"? seems like the only part of your post that addresses the question is "Real materials will follow this outline." and there is no source or reasoning Commented Feb 18, 2018 at 19:49
• Anna V @thnx 4 answering so elaborately. Its was very helpful to properly understand, the concept😊👌👍 Commented May 3, 2018 at 10:52