Solid state lighting (SSL) uses computer-chip-like crystals to emit light. The mechanism by which they generate light makes them efficient and controllable.

Light emitting diodes (LEDs) are semiconductor devices made in roughly the same way as computer chips. Their light doesn’t come from a heated wire or excited atoms in a vapor, instead it is emitted from a solid crystalline chip, which is why it’s called solid-state lighting. There are a few different processes that can be used to build semiconductors, but they all start by building a crystal.

A crystal is defined as an arrangement of atoms with long range order. Imagine a billiard table packed full of billiard balls, with no room in between. Then put on another layer of billiard balls, then another, each resting in the “pockets” where the balls on the previous level come together. If you know where the center of one billiard ball is, and the direction of the sides of the table, you know exactly how far to go to find the center of another billiard ball, in all three directions. That’s what solid state physicists mean by “long range order.” The long range order creates effects with far-reaching consequences.

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Originally published at Suite101, 29 MAR 2011

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