LED light is created in much the same way that light is created in a
flourescent tube. The electrons of atoms are pumped up to higher states,
and when they fall back down, light is given off. However, in an LED the
electrons are not in orbitals stuck to individual atoms. Instead the
electrons occupy a "sea of charge" and they wander among all the atoms in
the material.
Be aware that all substances contain electrons. The electrons I'm talking
about are not supplied by the battery, they instead occur naturally in the
wires, crystals, etc.
To create light, two conductive crystals of different characteristics are
connected together. Both types of crystal contain movable electrons. In
one type of crystal the electrons "orbit" at a high energy level, and in
the other, they "orbit" low. When a voltage is applied across the joined
crystals, the electrons inside are forced to flow across the boundary
between the pair of crystals. If the flow direction is correct, electrons
in the "high" crystal flow into the "low" and must drop to the lower
energy level. As they do, they give off light. The frequency of the
light (which we see as the color) is determined by the difference in
energy levels between the two crystals. By making different types of
crystals having different energy differences, various colors of light can
be created.
The "high" and "low" crystals are usually called "n-type" and "p-type".
In n-type crystals the electrons exist in an outer orbital energy level,
and during an electric current they travel at this level. In "p-type"
crystals the electrons exist at a deeper orbital level. When connected
properly in a circuit with a battery, the battery takes electrons from the
low energy level of the p-type crystal and pumps them up to the high
energy level of the n-type. The electrons then flow across the crystal
junction, fall down in energy and emit light, and end up back in the
p-type crystal.
LEDs are much like solar cells, but in a solar cell the process runs
backwards: light causes electrons in the p-type crystal to jump upwards in
energy. If these electrons are near the crystal junctions, they can end
up in the n-type crystal, and they can flow through wires to the outside
world.
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William Beaty voice:206-781-3320 bbs:206-789-0775 cserv:71241,3623
EE/Programmer/Science exhibit designer http://www.eskimo.com/~billb/
Seattle, WA 98117 billb@eskimo.com SCIENCE HOBBYIST web page