The twinkling lights of Christmas are not just the ultimate test for your untangling skills but also apparently a shimmering symbol of joy and warmth. Behind their sparkle is a dance of quantum physics that most of us don’t think about as we wage war with the knot of lights from last year. As we deck the halls with these stubborn strings of defiance, each bulb stands as a tiny but mighty tribute to human cleverness and the whimsical ways of the quantum. From the days of yore with their flickering candlelit charm to the modern LED wonders that won’t burn your cat’s whiskers, the evolution of Christmas lights is as enthralling as finding that one working bulb in a chain of darkness.
Long before the advent of Christianity, plants and trees that remained green all year had a special meaning for people in the winter. Just as people today decorate their homes during the festive season with pine, spruce, and fir trees, ancient peoples hung evergreen boughs over their doors and windows. In many countries, it was believed that evergreens would keep away witches, ghosts, evil spirits, illness, and Amazon package thieves. The Christmas tree as we know it started in Germany during the 16th century when devout Christians brought decorated trees into their homes, where it was much warmer, especially with the introduction of candles.
This leap in festive luminescence began in the 16th century when the first tapers were carefully affixed to the branches of trees, bringing the starry night sky into the home. It was a precarious beauty, with each flame meticulously watched to prevent a merry blaze lest one end up as a cautionary German Brother’s Grimm fairy tale instead of a Yuletide carol. But the appeal of a tree that glowed with light was irresistible, and the tradition flickered to life across Europe. As the tradition crossed the ocean during the American Revolution, it found its way into the hearts of the New World. American soldiers stationed with German mercenaries saw the light, literally and metaphorically, as they were introduced to the candlelit Christmas tree. This quaint European custom quickly took root in America, where it would eventually be supercharged by the spirit of innovation, progress, and Black Friday sales.
Christmas Tree 2: Electric Boogaloo
As the 19th century dawned, the flame-lit fir found itself on the cusp of an electric revolution. Enter Thomas Edison, the wizard of Menlo Park, who, after having a literal light-bulb moment, decided to show off his invention by lighting up a Christmas tree with electric bulbs for the first time in 1882. This was not just any tree, but one with 80 red, white, and blue walnut-sized light bulbs, making it the season’s must-have item. The tree itself was stood up in the home of Edward Johnson, who took the following photo with what looks to be an iPhone.
Yet, it took a while for electric Christmas lights to catch on, as early adopters had to be both wealthy and brave enough to welcome electricity into their homes — a concept still as mystical and unnerving as a visit from St. Nick himself. But as the 20th century rolled in, so did the affordability and popularity of electric lights, ensuring that the Christmas tree would never again be left in the dark. Soon, department stores began dressing up windows with dazzling light displays, turning city streets into rivers of light, a prelude to the modern holiday season that glows with the true spirit of Christmas: consumer capitalism.
Every year around this time, various fire departments stage a demonstration reminding people to water their Christmas trees so they can safely play with blowtorches around them. While it is somewhat obvious that placing an open flame smack dad on top of sprawling kindling is a bad idea, electric lights don’t entirely remove the risk of turning your holiday decorations into a Santa Claus effigy.
The Incandescent Era
Incandescence refers to things that emit light when heated. If you’ve ever touched a lightbulb, especially one of those large ones in your grandmother’s house, you’ll have immediately regretted it. The heat from a lightbulb is not so much the effect of lighting your house but the cause of it. Inside each bulb, a tiny wire filament performs a heated high-wire act, teetering between illumination and incineration. This is seemingly the work of thermodynamics and electromagnetism. The filament is a resistor, which acts like friction against electric current. This friction, like that of rubbing your hands together or the sexual tension between Ross and Rachel, creates both heat and season finale cliffhangers. When the temperature reaches a few thousand degrees (yep, that hot), it gives off light, which is why hundreds of Christmas tree fires still occur every year.
Though we didn’t need quantum physics to create lightbulbs, this effect of heat-created light is exactly why quantum physics was invented in 1900 by Max Planck. You see, there is just no way to explain why hot things emit light the way they do using 19th-century physics. It took Planck and an entourage of young upstart physicists to completely re-invent our conceptions of matter and energy. The core idea is that energy comes in discrete chunks, called quanta, instead of “flowing” continuously. What that has to do with a lightbulb is certainly not obvious, but trust me (or a bunch of people with Nobel Prizes) that it’s necessary.
Now, incandescent bulbs produce light but also, unfortunately, a lot of wasted heat. It was a cozy inefficiency that wouldn’t stand the test of time or prevent the hundreds of Christmas tree fires that still occur every holiday season. It is true that quantum physics explains lightbulbs, amongst many other things, but its real power lies in guiding the engineering of new kinds of light and matter never before seen in the universe.
The basic idea of quantum energy is this: things have energy levels that look like steps on a ladder. When they move up and down, they absorb or emit a quantum of energy. If the energy is emitted as light, it is called a photon. The energy of a photon is related to its wavelength (symbolized by the Greek letter nu: ν) through the universal constant h, called Planck’s constant. You may recall that the wavelength of light determines its color — red is about 450 nanometers, while blue light is about 650 nanometers.
Turning physics into engineering means designing materials and devices with specific energy level patterns that produce exactly the kind of light required. Enter the LED, which stands for Light Emitting Diode. Again, it’s not so much that quantum physics explains how LEDs emit light at the atomic level, which it does, but that quantum physics told us how to engineer such devices to do it. Electrons move between energy levels within an atom, and as they drop from a higher energy level to a lower one, they release photons with exactly that energy difference.
The first visible-light LED was invented in 1962. It was red. But it wasn’t bright or efficient. It wasn’t until the 1970s that high-brightness, high-efficiency red LEDs were developed. By the end of the decade, red LEDs were widely available, creating new applications of the technology in things like calculators and digital watches. Other colors came along, but it wasn’t until the mid-90s that high-brightness blue LEDs were created. While the early efforts were scientific, by this time, it was industrial research. Nonetheless, it is quantum materials science that powered the LED revolution, not to mention the rest of the digital age!
With red, green, and blue (RGB) light, we can match the three color-perceiving cones in our eyes. While it is often said that red, green, and blue make white, that’s not quite true — it’s just that our paltry sensors on these meat sacks we shuffle around can’t tell the difference between “true” white light (a perfect mix of all frequencies) and the combination of just three frequencies. But let’s not quibble over color theory at a quantum party.
Quantum energy for the win
Let’s not forget that before the LED revolution, we were at the mercy of the incandescent bulb. These bulbs were the divas of the lighting world — like miniature Gary Busey’s, they are high maintenance, not very efficient, and always burning out at the worst possible times. They only transform about 5% of their energy into visible light, which is great if you’re a lizard stuck in a glass house but not so much if you’re trying to light your living room without turning it into a sauna.
In contrast, LEDs are the calm, cool, collected types. They’re more like the Ryan Goslings of light production — compactly designed, effortlessly efficient, and oh-so versatile. LEDs typically convert about 15% of the input electrical energy into visible light. Because they can be embedded into electronic chips, they can now be found everywhere, including the ever-growing product line of illuminated Christmas decorations.
The LED revolution is a story of how quantum physics, with its steps, energy ladders, and photons, went from chalkboard scribbles to lighting up our lives. It’s a tale of scientific persistence, a bit of luck, and a whole lot of quantum wizardry. We are still far from the theoretical limits of efficiency for LED light, so there is lots of room for improvements and innovative new applications.
What I’m trying to say is let’s raise our glasses of rum and eggnog to the quantum physicists of yore and to those at the cutting edge. As we wrap our homes in the efficient glow of LED Christmas lights, we’re not just participating in a holiday tradition — we’re also witnessing the wonders of quantum physics in action.
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Dr. Chris Ferrie