First try

The EC default current for its LEDs can be seen in its settings as 20mA. It shows as blown when the current through it is double that setting (ie 40mA). You can alter its volts and current in its settings if you wish. It is normal procedure to put a resistor in series with an LED at all times... Choose a resistor value which keeps the current at 20mA or just below for this EC LED default setting. e.g....Make this battery 12v, put in a resistor and view the current shown. Then alter the resistor value until the LED just turns from blown to green. What is the shown current there now? Then adjust the resistor until the current is 20mA or a little less.

V=IR .... so if you chose a 500 Ohm resistor to achieve the 20mA (ie 0.02A) current, then V= 0.02x 500 which means that V=10 across that resistor .... leaving 2v across the LED (as per settings) .... thus making 12v total as per the battery.

Actually the LED blows at 2.08v

@LilKirby77... look at the current at 2.07v then look at it again at 2.08v .... between those two voltages is when the current reaches the 40mA which I described.

It depends on the temperature

@rich11292000 ... perhaps so, but not here on EC regarding the mentioned queries.

EC is trying to teach good habits, ie, a 20 mA LED is a 20 mA LED..

The LEDs on here are sort of "ideal" LEDs. Real LEDs have a range of forward voltage drops - they're certainly not all 2 V, and the Vf is partly dependent on the colour emitted by the LED. To oversimplify a bit, the longer the wavelength (the "redder" the LED), the lower the Vf. A red LED will drop around 1.6 - 1.8 V and a blue one (or a white one, which often is really blue) anything up to 3 V, maybe a bit more. Real LEDs also vary widely in what current they'll take. I have commercially-available LEDs in my parts box which give a more than respectable light at 5 mA; the designers of this simulator have decided that their simulated LEDs should default to 20 mA with a "blow up" current of twice the default. If you want to model real life LEDs you'd need to measure the current for a desired light output for your selected real LED, measure the Vf for your selected real LED, and set the simulated LED accordingly. You don't always need a current-limiting resistor, by the way; if the Vf for your LED is equal to the supply voltage you'll get away without one. Often a series string of LEDs is used to achieve this - for instance a cheap 12V LED for a car interior light bulb might well consist of a few strings of 4 LED chips connected in series (4 LEDs @ 3 V giving a drop of 12 V).

Some real life LEDs: http://everycircuit.com/circuit/5325247069028352

Shit

This app requires Resistance to emulate properly, as in real life anybody would advise using resistance in order to prevent components overheating

Here

http://everycircuit.com/circuit/5889796366139392