willduino:
Can someone please explain why in the scenario with 3 LED's in series, the voltmeter would show ≈0.4V when checking them individually but then give a higher total voltage?
Take a photo of your measurement for your single LED - including the LED and the multimeter reading. This measurement was taken with a 9V DC supply and a series resistor for limiting the current right?
It is a good idea to know the specifications of this LED. Or you could assume a particular forward voltage, and then you could use a variable DC voltage supply (eg, a bench power supply) to wind up the DC voltage (and use a suitable half-watt 220 Ohm resistor in series) until you get some illumination. But don't wind up the voltage too much, or else it might destroy the LED and/or resistor. Then you could maybe measure the current and get an idea of what level of current this LED can operate at. That's if you don't have specs for this LED.