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 i

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.)