[Marv’s Lab] setup is on a nice PCB that uses a rotary switch to select between 5 LEDs of different wavelengths, with banana plugs for the multi-meter ... for current measurement, so the volt ...

Figure 4 Measure the voltage across a zener diode with a digital multimeter. You can use the circuits in figures 2 and 3 to test LEDs, regardless of their color. Place the forward-biased LED you would ...