DIY LED Parts

Solid, 20 gauge. I use the hookup wire from a company called Vetco (tinned copper) but you can use the Radio Shack stuff, or doorbell wire from Lowes.

If you break down this diagram to where the voltage drops occur, the only LEDs that would light are 6, 1 and 5 actually.

LEDs won't conduct current until a voltage differential is present. But if you fix the voltage and vary the current, you get into trouble because the actual voltage drop will vary in a very tight window because of heating affecting the characteristics of the chip. So you could fix the voltage (using a constant voltage power supply) but then you're trying to match the required voltage drop (to get a certain level of output) and that is a moving target.

So the answer is to fix the current and let the voltage do what it needs to do (i.e. constant current power supply that applies whatever voltage is needed to maintain a given current). You can't (easily) control LEDs by using a fixed voltage, which is why no one does it. Which is also why using resistors to try and manipulate the voltage is a bad idea in general. Resistors are useful in the other example where you have parallel strings that are splitting current from a source like in the DT fixture example (with the fuses and 3000mA source current) but in that case, you would be measuring the voltage drop across an individual string at various points of operation (cool, warm, hot) and then seeing what string has a lower Vdrop and adding in a resistor to bring that string up to match the other ones so that there is balance when you put the 3 strings together. Most people then under-drive the strings to make sure that they're OK if one string gets more current due to heating effects (i.e. using LEDs rated for 1500mA and pushing 1000mA current)

So can you tell that I've had my fair share of EE classes? Not that I ever used them after college until I started building LED fixtures! (I have a BS in EE)