There’s an excellent reason LEDs have taken on the aura of inevitability: LEDs are semiconductors, and like all solid-state technology, they are getting better and cheaper on a predictable curve.

In 1999, a researcher named Roland Haitz, then heading up semiconductor R&D at Hewlett-Packard, coauthored a paper that became the lighting industry’s manifesto. By charting the historical prices of LEDs and projecting forward, Haitz estimated that the amount of light they produced would increase by a factor of 20 per decade, while the cost would correspondingly drop by a factor of 10. Haitz’s law has proven remarkably accurate.

But the lighting industry still has major hurdles to clear before LEDs gain acceptance by consumers.

So the LEDs found in current household applications are blue diodes daubed with a powdered coating called a phosphor, which includes rare-earth elements that filter blue light. The phosphor is generally yellow

Cooling is essential because hot diodes don’t last long.

Getting an LED to cast a light in a shape that will properly illuminate a room is perhaps an even more difficult challenge. LEDs are point lighting sources