Warner Bros.

The massive lighting display Clark Griswold puts up in the holiday classic National Lampoon’s Christmas Vacation is a sight to behold and a key part of the plot. But how much electricity did it use?

First, Let’s Establish Some Basic Premises

Anytime you’re diving into a bit of movie forensics, you always have to establish the basic premises you’re working with because without that, the combination of suspension of disbelief and movie magic can make conducting any calculations nearly impossible.

National Lampoon's Christmas Vacation

It's not just a classic Christmas comedy, it's a crash course in holiday lighting safety.

So what do we know about the Griswold home, the mid-century Colonial-style house that serves as the primary set of the popular 1989 film?

We know that the home, within the context of the movie, is located in a suburb of Chicago (although in real life, the house is actually located on Blondie Street, an outdoor backlot set located on Warner Brothers Ranch in Burbank, California).

Based on the movie’s time period (the late 1980s) we can assume a few things about both the home and the lights Clark drapes all around it.

First, we can guess what size electrical service the Griswold home has. Based on the age of the home and the time period, it’s likely that the electrical service is either 60 amps (if installed in the 1950s or 1960s) or, perhaps at some point, upgraded to a 100 amp service if the electrical panel was replaced closer to the time of the film. We briefly get a shot of the electric meter outside the home showing the meter spinning wildly when the lights are on.

A power meter lit by Christmas lights.
Warner Bros.

The meter is an old Landis & Gyr Duncan analog meter rated for 200 amps. However, we can’t draw any real conclusions from that because 200 amp meters are common—my older home has had a 200 amp meter for decades and only got a 200 amp service when I updated it in 2021.

Second, by Clark’s accounting, there are 25,000 lights on the house. That’s likely a wee bit of an exaggeration, but we’re going to run with it (and do our best to throw out a realistic estimate in a moment).

Third, we know LED holiday lighting wasn’t a thing in the 1980s, and all of the lights on Clark’s house are incandescent bulbs in the then-very-popular large C9-style.

Not only do we see the C9-style bulbs close enough to identify them several times in the film, but the boxes that Clark and his son Rusty unpack are labeled “C9 Christmas Lights.” Given the numbers we’re about to throw at you, we can assure you that Clark Griswold certainly wishes he could have saved money with LED Christmas lights.

Finally, we know the average national price for electricity was 7 cents a kilowatt hour during the time the film takes place. With all that information, we can run the numbers.

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Next, Let’s Get Calculating

There are a couple of ways we can look at how much electricity Clark used, ranging from taking him at his word to inferring usage based on clues in the movie and the limitations of his home.

How Much Would 25,000 Twinkle Lights Use?

In the film, Clark proclaims the house is decked out with”25,000 imported Italian twinkle lights.” At 7W per bulb, that works out to 175,000 watts (175 kW). Putting aside, for a moment, the secondary concerns like whether or not his home could handle that load, let’s just deal with the raw numbers.

At 1989 electricity prices, that means Clark’s display uses $12.25 per hour. Run from, say, 6 PM to midnight every day, it would cost $73.50 per day. If run for the month of December, it would cost $2,205. Adjusted for inflation, that’s around $5,294.

How Much Could a Clark’s Electrical Service Support?

We can estimate how much the electrical service of Clark’s home could support based on what kind of service he had.

If he had a 200-amp meter paired with a 60-amp service, un-updated since the home’s construction, it would max out at 14,400 watts.

A 100-amp service would max out at 24,000 watts, and a 200-amp service would max out at 48,000 watts.

We know a strand of C9 bulbs has 25 7W bulbs, thus consuming 175W. Assuming that Clark’s home has a minimum overhead load of 1,000W (for the fridge, lights, furnace blower, etc.) that leaves us with 13.4 kW, 23 kW, and 47 kW, leftover, respectively, for the lights.

Dividing by 175 and rounding down, that means depending on the size of his electrical service, Clark could theoretically run 76 strands with 1,900 bulbs, 131 strands with 3,275 bulbs, or 268 strands with 6,700 bulbs.

Even if Clark had a completely separate service run to his garage just for such projects, he’d still fall short of the 25,000 light goal by a substantial amount. Missing that goal is probably for the best, because the entire Griswold setup was a giant fire hazard.

What Would Trigger an Auxillary Nuclear Generator?

A worker at a nuclear power plant activating an auxillary energy source.
Warner Bros.

When Clark finally gets the lights working, the power grid buckles under the strain, blacking out first his neighborhood and then the surrounding city. Briefly, you hear an alarm and see somebody at a power plant flip a giant switch labeled “Auxillary Nuclear.”

The city of Chicago is, in fact, powered by a nuclear power plant. And that power plant was fully online and operational in 1989. The plant, Byron Nuclear Generating Station, can generate 2,347 MW of energy. If we assume that the giant theatrical “Auxillary Nuclear” switch was activating the recently completed Unit 2 portion of the Byron plant expressly for the purpose of keeping up with the demand Clark created, the demand would be 1136 MW.

But it turns out there are other people in the world as curious about the power consumption of Clark’s house as we are! While some folks stop their calculations at the “25,000 twinkle lights” stage, we forge ahead. And some people forge even farther than we have.

You can read the analog dials on an old power meter to determine how much energy your home uses. It’s an old trick we shared in our guide to measuring your home’s energy use. A 2014 blog post from an equally curious person used that very trick to calculate how much energy the Griswold home is using while the lights are on based on how long the meter is visible and how many times the various dials rotate in that time frame.

We have to assume that the clip was sped up for theatrical effect because if the meter was spinning in real time, ol’ Clark’s house was sucking down 529 MW—or about as much power a quarter of the greater Chicago region. So whatever the activation of auxiliary power did in the film, we can safely assume it delivered that much extra power to the grid.

If all this talk about spending a bunch of money on Christmas lights has you thinking about the matter more seriously, now’s the perfect time to learn about the pros and cons of LED Christmas lights. And while you’re at it, slap a smart plug on your Christmas lights to ensure they’re on when you want them and off when you don’t.

Profile Photo for Jason Fitzpatrick Jason Fitzpatrick
Jason Fitzpatrick is the Senior Smart Home Editor at How-To Geek. He has over a decade of experience in publishing and has authored thousands of articles at How-To Geek, Review Geek, LifeSavvy, and Lifehacker. Jason served as Lifehacker's Weekend Editor before he joined How-To Geek.
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