Hi peej, The following quote is from the URL link further below. It is for regular diodes but this should also apply to LED's. Current will always 'seek' the least resistance path and since it is hard to find identical diodes (or LED's) it will choose one of them and start the following process.It works like an endless cycle which ends up with only one diode conducting or broken down. The more current, the more heat; the more HEAT, the more CURRENT, and so on. If you get lucky with well matched LED's and nothing happens, you will at least have one LED brighter than the others.
Ah, that's a lot simpler.You can buy LED strips that are powered from 12V, with built in resistor & everything.All you need is a buffer chip like ULN2803 to control the ground to turn them on & off.https://www.adafruit.com/products/357
I've had the transistors since 1983 or '84, little drawerful of them, and decided I was finally going to use them for something, so I did.
Sometimes a single transistor or two (and associated resistors) is all you need.For example, on this board (in various stages of construction) I used 4 transistors and 11 resistors to control 4 strings of 5 LEDs each, 1 string of 3 LEDs, 1 LED, and to invert a signal.A ULN2003 or 7406 with 4 resistors would have done the same. I've had the transistors since 1983 or '84, little drawerful of them, and decided I was finally going to use them for something, so I did.