Figure 1 - 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.

This trend is known as 'Haitz's Law' after Roland Haitz, the scientist from Agilent Technologies who first analysed this behaviour. Open symbols denote cost per lumen (measured in US dollars) and closed symbols denote flux per package (measured in lumens).