LED current seems to be one of those things that there is loads of poor information about. Often circuits take no account of component or power supply variation.
For instance searching for "led calculator" comes up with this page **broken link removed**
The calculations take no account of variations and are often wrong.
If you ask for an array of 8 LEDs at 2 V each, running from 12 V at 10 mA, the first suggestion is to put 6 in series with a 1 ohm resistor, then 2 in series with an 820 ohm resistor.
Change the current to 1 mA, and the 6 LEDs still need a 1 ohm resistor, while the 2 now need 8200 ohms.
The configuration is really bad for real-world conditions, where 6 LEDs in series on a 12 V supply, with effectively no series resistor could have just about any current. All LED arrays where the current is controlled by the resistor should have at least 10% of the supply voltage dropped across the resistor, and more if the supply isn't well regulated, but that rule isn't instituted in the calculator.