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. //

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.