I'm not an expert (just a physics prof), but my understanding is that LEDs always emit one specific color (wavelength) of light rather than white light (which is a mixture of many wavelengths). So if you want to use an LED to produce white light, you set up a material that absorbs light at one wavelength and then re-emits it in a wide variety of wavelengths (that is, the phosphor).
(This is also the way that fluorescent bulbs work: the hot mercury vapor inside produces invisible ultraviolet light, but the phosphorescent coating absorbs that UV and re-emits it in a range of visible wavelengths. And it's no coincidence that they're using a blue LED with a short wavelength: in general, a phosphor can only re-emit at longer wavelengths than it absorbed. That may imply that these bulbs emit little or no violet in their "white" light, since violet has a shorter wavelength than blue.)
If it uses a phosphor coating, isn't it also prone to the same issue of diminishing lumens over time as the CFLs? These bulbs lose up to 30% luminosity in 6 months (the tri-phospor ones, more expensive, can a last a year begore losing 10%/20%).
If they lose power like CFLs, even though the warranty is 10 years, you may be forced to replace it way before that.
I don't think I can comment on that with any authority at all. Is it possible that using a blue light as the source rather than UV reduces the degradation of the phosphorescent coating?
1) put red, green and blue LEDs in the same package and either bring all the connections outside for an external balancing circuit (which also lets you do multicolour effect), or balance the currents internally and just bring out two connections.
2) make a blue LED (with substantial UV output) and use a phosphor coating to re-emit "white" light. This coating appears very yellow when the LED is off, and is similar to the way a conventional fluorescent tube works.
2) is cheaper and more efficient, but only emits "white" light - the trick is getting it to not appear too blue as the phosphor doesn't absorb all the blue light.
EDIT: also, the white light from (1) is not really very white - the spectrum is hard to tailor compared to using a phosphor.
Basically, LEDs are typically mono-chromatic, i.e. they generate light within a pretty tight range of wavelengths (what we perceive as color).
There are two ways to get white light (which is light of "all" visible wavelengths) from a LED: combining a red, a green and a blue LED, or using a coating that when energized by (typically blue) light, in turn reacts and emits white light.
LEDs emit light in a narrow frequency band, i.e. LEDs have intrinsic colors. White is not just one color, so your options to make white light from LEDs are:
1) Use multiple colors of LEDs, which will make the light source look white but objects lit by this source will have off colors.
2) Use a phosphor coating on the LEDs, where the phosphor absorbs (most of) the narrow frequency band output by the LEDs and emits the color(s) that you want.
In this case, they went with option 2 with a phosphor that absorbs blue light and emits broad spectrum white light.
Based on the material used an LED produces a specific colour (wavelength). To create white light you need to emit light at all wavelengths simultaneously.
White LEDs work by emitting blue light but being coated in phosphors that emit the other colours when hit by that blue light.
Often you'll see that white LEDs appear a little "cold" in colour which is caused by the slight excess of blue light compared to the phosphor generated other wavelengths.
White light is the combination of many spectrums of light. On your monitor for example, it is red + green + blue.
LEDs however, only output one narrow spectrum. So, to solve this issue, the "white" LED is really a Blue LED + a material that converts the color blue into white.
Could someone explain that a bit more please?