Light Emitting Diodes, as the name states, are diodes. A diode is a semiconductor device that permits current flow in one direction. Semiconductor diodes are a junction of two materials. One material has a surplus of positive charge (the term ‘holes’ is used to indicate the absence of an electron, the reason for the positive charge), and the other a surplus of negative charge (electrons).

When you take that PN junction and apply a forward voltage, electrons and holes are brought together. They combine near the junction, and this releases light energy—the “light emitting” part of the name.