SandAndAlum t1_jecchs7 wrote
Reply to comment by ddr1ver in The New Light Is Bad: There’s something off about LED bulbs — which will soon be, thanks to a federal ban, the only kind you can buy. by newzee1
LEDs are by no means monochromatic. And most use phosphors on a blue LED, not multiple LEDs.
ddr1ver t1_jecx6bk wrote
That’s not the way I learned it.
“Table 1 shows, different LEDs have different emission spectra: each with a very thin emission spectrum. LEDs only emit one color of light not because they have colored plastic over white light, but because they only emit light at a single wavelength.”
https://sites.tufts.edu/eeseniordesignhandbook/2015/leds-technology/#
SandAndAlum t1_jed240z wrote
http://i.stack.imgur.com/6kuZf.png
Blue LEDs are much more efficient than most other colours and having three sets of voltage control or three seperate circuits is more expensive. Plus "single wavelength" is only even approximately true of a laser. Those spectra you linked to are still a fairly broad range (to the point where red and green can even be somewhat distinct under an orange LED even if both are very orange-ish).
Additionally your source describes a modern white LED
> The other method of creating white light is known as spectrum adjustment.
> Spectrum adjustment happens when light is absorbed and then re-emitted again. By doing so, the color and appearance of the light can be altered. There is a caveat, however, that the light can only be shifted to larger wavelengths. If a material were able to absorb a long wavelength of light and emit the same amount of a shorter wavelength, this would violate the conservation of energy. This is why it was not possible to generate blue light from other diodes. However, the reverse process does in fact work: if a blue diode is passed thorough a yellow phosphor, the blue and yellow combine into a white light well suited for everyday tasks.
RGB LEDs are at least three (and sometimes four) LEDs though.
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