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
Due to the way LEDs actually create light, longer wavelengths of light (like red and green) are much easier to create. That’s why red LEDs were invented first, followed by green. Blue, and violet were impossible until researchers made a breakthrough in how to actually build the structure of the LED on a microscopic level. Even then, blue LEDs were a whole lot dimmer for quite a while than the red and green ones we’re used to. Commercially viable blue LEDs weren’t available until the late 1980s or early 1990s.
For a much more in-depth (yet still mostly approachable) explanation, [check out this video from Veritasium](https://www.youtube.com/watch?v=AF8d72mA41M).
EDIT: Interestingly enough, many commercial white LEDs are actually blue LEDs with a yellow phosphor coating on them.
Latest Answers