Although solid-state lighting has made significant headway in the lighting industry and fixture marketplace, there is still a sufficient amount of technical performance data that is unknown and untested when it comes to this new technology. An article in the August 2009 issue of IEEE Spectrum, a publication from the Institute of Electrical and Electronics Engineers, calls attention to a problem specific to LEDs known as “droop.”
Droop is a phenomenon experienced by blue (nitrate) LEDs—the LEDs that are used to produce white light. As the diode's power level reaches an output sufficient for general lighting applications, the efficiency of the LED declines significantly. To maintain this amount of light output, you have to continue to feed the LED more and more power. In effect, this cancels out any potential energy savings this much-touted nonfilament light source might provide, and highlights the fact that LEDs perform best at low power. This puts a very different spin on the information that lighting manufacturers have been promoting as they race to announce and outdo one another with higher lumen-per-watt totals.
No one knows for sure why LEDs experience this technical anomaly, and scientists and engineers are hard at work to solve the puzzle. Some researchers attribute it to the electron structure of the diode, but there is no general consensus. One thing is for sure: now that this technical truth has been revealed it adds yet another hurdle for solid-state lighting to overcome as it tries to prove itself as a lighting technology with long-term potential.