Out of pure curiosity, I purchased a LED string powered by 2x AA cells. There are 20 LEDs, all wired in parallel and in the sequence Blue, Green, Yellow, Red,- repeated 5 times. There are no other visible electronic items such as dropper resistors, and certainly no inverter of any kind.
When connected to a variable supply the string has this characteristic:
The slope of the curve suggests an equivalent series resistance of 1.5 Ohms, or 30 ohms if each LED has its own series resistor. The LEDs all shine with roughly the same brightness.
I'm just curious to know why this works, given that red and blue LEDs normally have quite different forward conduction characteristics?
The ESR of your average cheap AA cell probably provides sufficient current limiting but wouldn't a red LED win the current battle if directly paralled across a blue LED (which I thought required a good deal more than 3v, anyway)?