How light emitting diodes, LEDs, works! Continued Page 2

To create LED light, first we connect two conductive crystals of different
characteristics together. Both types of crystal contain movable
electrons. In one type of crystal the electrons "orbit" naturally at a
high energy level, and in the other, they always "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" crystal and must begin orbiting at the lower energy level. As they
fall to the lower energy level, 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 manufacturing different types
of crystals having different natural energy levels, various colors of
light can be created. Crystals with similar levels create low-energy
photons of red light or even infrared light. With a larger difference in
energy levels, green light can be created. An even larger energy-step can
create blue light.

The "high" and "low" crystals are usually called "n-type" and "p-type."
In n-type crystals the movable electrons wander around while staying at
the upper energy level of an unfilled outer atomic orbital. During an
electric current they travel at this level. In "p-type" crystals the
mobile electrons naturally exist at a deeper orbital level. When the two
crystals are connected to each other and then connected properly in a
circuit with a battery, the battery creates a current in the entire
circuit. It sucks electrons out of the end of the p-type crystal and into
the wire. At the same time it pushes electrons into the far end of the
n-type crystal. The electrons already in the n-type crystal then are
forced to flow across the crystal junction, fall down in energy, emit
light, and end up back in the p-type crystal.

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