Well, it is a *very* bad demo in my opinion.
I equate it to describing the birth of children to deliveries of babies by the stork.
It completely misleads the viewer, and shows the utter lack of understanding of how things work.
Light is not emitted when a hole "flows" or transits across the device and the hole, (which is not a physical particle, but actually the lack of an electron) and electron meet and emit a photon.
Wrong.
Photons are released as a result of moving electrons. In an atom, electrons move in orbitals around the nucleus. Electrons in different orbitals have different amounts of energy. Generally speaking, electrons with greater energy move in orbitals farther away from the nucleus.
For an electron to jump from a lower orbital to a higher orbital, something has to boost its energy level. Conversely, an electron releases energy when it drops from a higher orbital to a lower one. This energy is released in the form of a photon. A greater energy drop releases a higher-energy photon, which is characterized by a higher frequency. (Check out How Light Works for a full explanation.)
As we saw in the last section, free electrons moving across a diode can fall into empty holes from the P-type layer. This involves a drop from the conduction band to a lower orbital, so the electrons release energy in the form of photons. This happens in any diode, but you can only see the photons when the diode is composed of certain material. The atoms in a standard silicon diode, for example, are arranged in such a way that the electron drops a relatively short distance. As a result, the photon's frequency is so low that it is invisible to the human eye -- it is in the infrared portion of the light spectrum.
(lifted off of
http://science.howstuffworks.com/led2.htm to keep things simple)
Basically, in a nutshell, *ATOMS* emit light when electrons drop from a higher to lower orbital, not from the combination of a plus and minus charge...sheesh
Quantum dots, a new laboratory method, work a bit differently. Will be interesting to see how well they work when they eventually get to market.
I hope folks remember orbitals, sub-shells, valence bands and conduction bands from high school science...