@jmwright Hi Jeremy: Not everyone can be an expert in all things (I suck at plumbing and roofing). With my BSEE degree as background, I refer you to this image:
In both circuits, one LED is being driven from 12V. The reason for the resistor in series is because the voltage drop of single LEDs is the same as it is for all diodes: .6 - .7V. Without the resistor, the LED would be over-driven. The resistor could be eliminated if 20 (12/.6) LEDs were being driven.
With 150V, many LEDs are used.