As far as I understand, you need to be able to mix red, green and blue light to get white light and replace lightbulbs. But the earliest example I can find of white LEDs used a blue LED and a yellow (apparently the result of mixing red and green light) phosphor coating to scatter the light across the visible spectrum. Why couldn’t something similar be done with a red LED and a cyan (mixing blue and green) coating/cover to produce white light instead?
In: Engineering
Phosphors can only downconvert wavelengths, not upconvert them. Fluorescent tubes downconvert UV light, and white LEDs downconvert blue light.
There are some fancy frequency doubling crystals that can go the other way, used in green laser pointers and such, but I believe they only work with laser light.
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