Something for Z. Efficiency drop-offs of LEDs explained.

From Popular Science http://www.popsci.com/science/article/2013-04/why-your-led-bulbs-give-terrible-light

A few paragraphs from the article...

Quote :

LEDs should be lighting the way to a greener future: They use 75 percent less energy and last 25 times longer than incandescent light bulbs, and they do so at a cooler temperature. But right now, we mostly use LEDs in electronics, because they have a bit of a drooping problem: at higher currents, the amount of light they produce takes a nose-dive.

LED-based lights contain a microchip with a positive-type and a negative-type semiconductor made of gallium nitride. Between the two, in a quantum well, the negative electrons from one semiconductor and the electron holes from the other combine, producing a photon of light. When you apply more electricity, it produces more photons--to a point.

In low power situations, like in your cell phone, the process works great. But when you raise the current up to the level it takes to light a room, nitride-based LEDs stop producing photons at the same rate. According to the research from UCSB's Center for Energy Efficient Materials, it's because the electrons collide with each other and lose their energy through heat instead of light.