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The P-N junction is also at the core of Solar cell electrical energy production. Photons knock the electrons over the P-N junction causing an electrical cycle to flow. Effectively the reverse happens with an LED.
This is the #1 challenge for the LED industry. Unfortunately LED is pure white light, so any light changes need to be made via filters. I do believe however if all combinations of the elements when tested may come up with the yellow light mmm maybe Au will throw a yellow light? (actually yellow/orange light is preferred by humans at night due to evolutionary reasons and the color of fire. White light is un-natural at night and leads to insomnia and proven increases in cancer in the long term.)
Interesting points you raise here. I use a tool to red shift the light on my computers at night to remove the blue light. It make a big difference on eyestrain and reduction of insomnia,