The Secret Of Twinkling Christmas Lights

With the holidays over, many of us are braving the elements to take down all those holiday lights. LED lights have largely taken over the market, but in some places, you can still get classic incandescent bulbs. There are some effects that LEDs can’t quite mimic yet. One of those is the magic of “twinkling” light sets, which [Alec Watson] explains in a Technology Connections video. Everyone has seen bulbs that flash, and strings that dim. But the twinkle effect until recently has been hard to describe.

Typical flashing bulbs use a bimetallic strip. As the filament of the bulb heats up, the strip bends, opening the circuit. Then the strip cools and closes the circuit again. Twinkling lights do exactly the opposite. The bimetallic strip shorts the bulb out rather than open the circuit. Twinkling sets also use a lot of bimetallic strip bulbs – typically every fifth bulb has a strip. The result of the bulbs being shorted out is that all be the bulbs in set see a higher voltage. This makes the entire strip shimmer in time with the flashing. That’s where the twinkling magic comes from.

It occurs to us that the voltage on the strip would be a great source of random seeds. Sure, you’d have to replace bulbs now and again, but how many people can say they get their random numbers from a set of Christmas lights?

If you’re curious how incandescent Christmas lights can blow and not take out the whole strip, check out this article about anti-fuses.

19 thoughts on “The Secret Of Twinkling Christmas Lights

  1. I don’t believe I’ve ever seen these types of lights before, and I didn’t think the effect was anything special when he finally got around to showing it. These things probably go hand in hand: if you’ve seen these types of lights throughout your youth you probably hold some kind of attachment to them.

    Seems like the effect wouldn’t be terribly difficult to replicate with LED if anyone was so inclined, but again, if it’s not popular enough to sell the original ones I don’t know anyone is clamoring to clone them either.

  2. “It occurs to us that the voltage on the strip would be a great source of random seeds”
    It might be a novel use for christmas lights but if you have a series of discrete switches that’s not going to provide anything close to a random distribution of voltage.

  3. This video was one if the most informative videos ever about Christmas lights. Thank you!!! I have purchased several sets of twinkling lights this year from different stores hoping to create a subtle twinkle on my Christmas tree. But none of them created the effect I really want. I like to run twinkle light strands down the inside of my tree and the rest are all steady lights. It creates a beautiful effect. But the twinkle has to be just right, and as you so perfectly described, the other types just don’t create the same ambience. So I’ll run by Ace Hardware tonight and see if I can snag a few. Like you, I’ll grab a couple of extras for future replacements in case we’re taking over by the LED light zombies. 😉

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  4. Bless you for this video. I have been looking for incandescent twinkling lights for about 10 years! Ever since LED lights started showing up in the stores I have been unable to find them. I cannot even find them online when I have looked. Now that I understand them, perhaps I can find some in estate sale lots or even online (now that I know I need bulbs that can take 2.9v).

  5. I am a huge fan of the twinkle lights and have been hoarding them whenever I come across them, but my husband is a fan of LEDs. The LED version of “twinkling” is a horrific flashing that would throw anyone watching them, into a seizure. The fading mode I just find annoying. Is it just that so few people know what a true “twinkle” light is, that they use the word for any light type that flashes? I’d love to see LEDs do a random twinkle mode, but I’m not holding my breath. Thank you for the video. It was very informative and enlightening.

  6. Very good video sir. Good explaination. As an engineer myslef, good to see your info. Hope other folks learn from it too.
    I have some of the twinkling strings, but am having a tough time finding replaement twinkling bulbs. Maybe you or some of your other viewers know of a place for some good deals on this type replacement bulbs. Thanks. RonB

  7. So here it is, November 14th, and we just put up our tree, fluffled it and started putting lights on it. Several years ago, I watched a video on Youtube from Rebecca Robeson (she’s an amazing interior designer and is well known for his Christmas decor). She turied me on to ‘twinkling’ lights. She said you can find them at Target. I promptly went to Target the next day and found them. This was back in 2014. They cost $7.99/box and the strand was about 15 feet. That was pretty pricey back then considering I wanted to buy five strands…but I did it anyway! They were from Philips and fast forward to now, and I cannot find them anywhere. I did buy another brand that claimed to be twinkling and was so disappointed. They twinkle was really fast the the color was way too white, compared to the Philips strand; it looked odd on the tree. But I like loading up the tree with ornaments so it does help blur the colors somewhat. I believe the ‘twinkling lights’ that I last bought were from Ace Hardware but they are just not as good as the Philips brand. As I’m writing this, it just occurred to me to reach out to Philips and see if they can help me further, to get more of these original, and amazing twinkling lights!

    1. I believe they can only be found in ‘vintage’ pre-90s. There is a ‘random *flashing*’ LED single-screw-in that some retail lights site claims is the closest thing currently in existence, at about two bucks a bulb. Why somebody doesn’t just make the damn things already is beyond me. This depresses me immensely. Still my C-7 ceramics are the best you’ll see in my neighborhood these days. Also a three-strander in which only one twinkles, and properly. (Hm. Possible the the two strands need a bulb or something?)

  8. Remember, Christmas lights were originally a series configuration. One goes bad, the others don’t light. In the early sixties, ours were like that, I think they’d been my grandparents’ lights. A few years later, we upgraded to modern lights, the bulbs in parallel so the others keptgoing if one went bad. So you could screw in bulbs that were bigger, and coated in foam, or bulbs that flashed.

    Having to check bulbs is a scene in Christmas Vacation, but I thought by then, series bulbs were in the past.

    Then a new wave of bulbs arrived, smaller incandescent that plugged in rather than screwed in. I thought those were back to series.

    Now LED bulbs, the ones I’ve seen don’t even have plugin bulbs.

  9. I have real twinkle icicle lights. Sylvania (model s2970x). They have a built in dial control and from that incorporate 4 individual stands within creating the perfect twinkle. I cannot find anything that comes close.

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