Vex LED Specs

What resistance do Vex LEDs have? How low can the supply voltage go before the LED stops working properly?
I’m using one as the load in a circuit, and I’d like to make sure I don’t damage it. I also want to know what my current draw will look like in my experiment.

It’s a diode, see the graph in this post.
https://vexforum.com/t/vex-leds-in-motor-port/30210/1

Usually with a LED you must provide an external current limiting resistor. What are you trying to do?

I’m testing the effectiveness of various acids as batteries. I’m guessing these would work for a resistor. Is this correct?

10 ohm would be on the low side, it all depends on the supply voltage (which if lower that about 2V will not turn the led on at all) Try using something like this to calculate the required resistor.
http://www.hobby-hour.com/electronics/ledcalc.php

Thanks! Do the LEDs actually use 20mA?

An LED will draw whatever current you have designed the circuit for, based on the voltage and resistance (remember ohm’s law E=IR ). 15-20mA is a typical design current for common LEDs without special provision to dissipate heat; therefore you adjust the dropping resistor to get the desired current. More than 20mA without special provisions, and you risk magic smoke.