An L.E.D. (Light Emitting Diode) is a
semiconductor device which emits light. You
may have heard of semiconductors, which are
used to make computer chips because of their
unusual properties. One of the unusual properties
is that they can be given different level of
positive and negative charges.
An L.E.D. is made by placing two different
types of semiconductors next to each other -
one, called P type, has extra positive
charges, and one, called N type, has extra
negative charges. The area between them is called
a junction. When the P side is connected to
one terminal of a battery, and the N side to
another, it forces electricity to flow through it.
When electrons go from the N side (where they had
lots of other electrons) to the P side (where
there are lots of extra positive charges), they
are attracted to the positive charges, and combine
with them. When they collide, the electron
loses energy as it stops moving, and this energy
is given off in the form of light.