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This might be a dumb question, but has anyone been able to successfully convert a built-in incandescent mini-light string to use LEDs? I have a few of these pre-lit burgundy-colored tinsel Christmas trees, which I like because not only does it eliminate the need to run a separate light string, the wire and sockets of the string blend in with the color of the tree, but obviously I'd prefer to substitute the lights themselves with LEDs if possible.

https://www.hayneedle.com/product/burgundy-tinsel-pre-lit-medium-christmas-tree-4-ft.cfm

https://www.hayneedle.com/product/burgundy-tinsel-pre-lit-medium-christmas-tree-75-ft.cfm?ltype=child&tid=GERS483-1

Again I'd like to keep the actual wire and sockets, but from what I understand, LED mini-lights rely on impedances in their special strings since the bulbs themselves are little more than the LED elements, so I'm curious if it would be safe to, say, splicing in the resistor canisters from off-the-shelf LED light strings or if doing that carries notable risks like starting a fire that could burn down my office building.

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  • \$\begingroup\$ Sounds like a lot of work to end up with lights that have traditionally been a pain in the ass. The lights are often connected in series (unplug one and they all go out) if so you should only need a single resistor but a rectifier would be wise because LEDs generally do not have much tolerance for reverse bias. \$\endgroup\$
    – Misunderstood
    Nov 11, 2018 at 3:31

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The LED strings typically have different sockets, since the LEDs are polarized and the incandescents (obviously) are not. If you can get the LEDs to fit the existing sockets, there's the issue of polarity - you'd need to probe each socket to determine which way round the LED should go in. The dropper resistor and diode (one, or a bridge) that come with the LED strings should be safe enough to swap onto the built-in string. Typically in LED sets, there are two or three separate strings, each with its own dropper and rectifier. I have one tree that has the incandescents built in, but I didn't attempt to do this, and just wound an LED string onto it in addition.

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  • \$\begingroup\$ I'd have to check the 7.5ft trees, but I took a look at the 4ft tree I have at my desk and it looks like it has 3 separate strings. Assuming for the moment that they're all the same length, I guess I'd have to cannibalize 3 50-light strings. \$\endgroup\$
    – Ian Bui
    Nov 9, 2018 at 21:38
  • \$\begingroup\$ And good point about LEDs being polarized. That slipped my mind and since you brought it up, that makes me wonder about the incandescent lights being designed to keep the rest of the string lit if any burn out. In addition to the string going dark if any lights are removed, I'm assuming that that means the lights are largely in series, thought possibly subsets of lights in parallel to each other with each light having a shunt wire. Anything else come to mind that I should look for? \$\endgroup\$
    – Ian Bui
    Nov 9, 2018 at 22:05
  • \$\begingroup\$ Incandescents are generally in fairly long strings, since the lower the voltage of the bulbs, the thicker the filament and they tend to be more durable, but since the forward drop of the LEDs is fixed, you can't typically have more than 40 or so in each string to stay under the supply voltage by enough margin that they're not just flashing at the very peak of the cycle, which makes flicker annoying. Incandescent bulbs have a little loop of wire around the filament supports that fuses to them when the filament fails to keep the rest of the chain lit, so that shouldn't affect the conversion. \$\endgroup\$
    – Phil G
    Nov 12, 2018 at 14:21
  • \$\begingroup\$ Oh okay, so it sounds like I should be mindful that any 50-light LED strings I find could possibly be grouped into subsets of 25 or so lights? Sounds like I'll have to abandon the idea for the 7.5ft trees since I wouldn't have time to convert them before I give the trees to other people this week. I still would like to convert the 4ft tree even though it's looking more and more like it something I would have to do for next year because of time and cost of materials and I might be better off completely removing the built-in strings and replacing them instead of trying to modify them. \$\endgroup\$
    – Ian Bui
    Nov 12, 2018 at 21:45
  • \$\begingroup\$ There's a big range of 'quality' of light sets, I have some that are far better than others in terms of flicker, I have some very good, and some very annoying ones at home, I'll have a look at how many strings they're in. I suspect that the 'bad' ones have a greater number. I think that in the end all you're going to be saving from the old set is the color-matched wire, given the issues with sockets. \$\endgroup\$
    – Phil G
    Nov 12, 2018 at 23:32

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