Haitz's Law

An observation of LEDs, that

Since the invention of the red LED in the late 1960s, every 10 years the light output per device has increased by a factor of 20 while the cost per lumen has fallen by a factor of 10.

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from The story of a new light source : Article : Nature Photonics.

In other words, every year, they just keep getting brighter and cheaper. Thus it begs the question: "When is it ever a good time to buy an LED lighting product?"

See also the Mike Wood article: LEDs: A Disruptive Technology.