[mturmon]

For more on the physics behind "white" LED's, there's a pretty good summary at:

http://en.wikipedia.org/wiki/Light-emitting_diode#White_ligh...

The fundamental challenge is that the wavelength of light emitted from the LED is constrained by the band gap structure of the diode. To get white-looking light, you need more than just one narrow frequency band.

For instance, until some new materials were developed in the 1990s, this is why there were no blue LEDs, only red, green, and amber.

[billswift]

Bob Johnstone's We Were Burning has a fascinating look at the development of the first blue laser diodes.

http://www.amazon.com/We-Were-Burning-Entrepreneurs-Electron...