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
With just red and green light, we can make anything in between. Even when mixing them, we can get oranges and yellows, but we can’t get white. We need blue to round out the spectrum to make white light.
The first white LEDs used this method, but it was a bit harsh on the eyes. Modern white LEDs light up phosphors on the inside of the bulb to make a wider range of wavelengths. The phosphors can only emit light in a longer wavelength than what activates them, so the green can’t fill in the gap above it, but the blue can fill in the gap below it.
It’s all a careful balancing act to make it easy on the eyes and look natural. It wasn’t until a few years ago that soft white LEDs could reach the point that they don’t bother me, and now I won’t use anything else between energy efficiency and the calmness of the light.
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