Red LEDs contain the flattest I/V curve earlier mentioned the knee. Nitride-dependent LEDs have a fairly steep I/V curve and are worthless for this intent. Although LED forward voltage is much more current-dependent than a Zener diode, Zener diodes with breakdown voltages down below 3 V aren't widely available. https://dallasqblwg.glifeblog.com/23495200/a-review-of-kosoom