There is no such thing as a "White LED", a LED is a monochromatic light source, it can only generate a light of a single color - as we know, "White" light - is a mixture of many colors
Our Sun, is a gigantic fusion reactor, converting 900 Million Tons of Hydrogen into 850 Million Tons of Helium every second - the 5 Million Tons left over, is made into light, heat, and other forms of energy
The White LED works in much the same way as a flourescent light bulb works, the Mercury vapor inside the tube has two lines of operation 275nm (Shortwave UV) and 365nm (Longwave UV) - as the electrons strike the side of the tube they excite the Phosphor on the side of the tube
As the Phosphor changes from a high energy state to a low energy state, a photon is released
Depending on the amount of energy that the electron raised the phosphor to, you get different colors - mostly random, and you get "White"
There are several different "colors" of white that are available in Flourescent tubes "Natural White" "Glow Bulb" "Black Light" and others, and they are just a different type of chemical for the phosphor coating on the walls of the tube
In the LED, the same process is happening, but instead of using Mercury Vapor (which is being used up in the process of the FL tube), they are using a BLUE LED (higher energy state) - the light output from the Blue LED - excites the Phosphor - and the same reaction occurs
Each company uses a different type of chemicals for its Phosphor, and as such - each company has a slightly different color spectrum on the white; and color temperature
Incandescent Light bulbs have been around for nearly a hundred years, and there have been great improvements in the technology of them
The original light bulbs had a vacuum inside instead of Argon, which caused them to "cloud up" the glass as the electrons struck the glass
White LEDs are fairly new, and I expect the same thing - over time, the chemical nature of the Phosphor will improve - and we will see higher Lumen/Watt output and better color rendition of "White"
Mike
www.inretech.com