@Hancock52 posted:Someone more expert than me can advise on this but I would have thought you’d have no voltage issue with warm white LEDs tapping into a strip of the same kind of bulbs. However, in my last project adding two very small (Z size) LEDs to a stock recent model (2020) Lionel LED overhead lighting strip to illuminate markers at the rear of the car, they dimmed down the strip in a way I did not expect. I swear by GRJ’s passenger car lighting modules, which are better than Lionel’s super-capacitor strips.
Paralleled LED's can be a problem unless they're exactly matched. Even two different brands that are both claimed as being a single color can react differently with operated in parallel. The issue is simply the sharp knee of voltage vs current for an LED, a slight difference in the manufacture of the chip can result in poor performance in parallel.
I routinely wire LED's in parallel, but only those from the same manufacturing batch. Others I use a resistor in series to equalize the currents. If you look at how the typical 12V LED strip lighting is constructed, there are three LED's in series with a small resistor in the 100-150 ohm range. The function of the resistor is to swamp out any minor LED characteristic and to insure each three LED segment is the same brightness.
I think many people have discovered that if you parallel a red and green LED that the red one lights and the green one doesn't. That's easily explained as the green LED has a higher operating voltage then the red LED. The chart below illustrates the issue. Note that the green LED at 20 milliamps requires about 3V, and the red one requires a bit less than 2V. Since LED's are a current mode device, if you adjust the current to 20ma for the red LED, the green one will never get to the voltage to light at all, or might light VERY dimly.
