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.

6 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.

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