Holidays Lights 2023: How Much Power?
As I’ve noted many times recently, instrumentation is addictive. Or perhaps it’s just my latest affectation? As I went about putting up our usual outdoor holiday lights, it occurred to me that I should change up how they are powered. In so doing, I’d collect some data on how much power is used by the festive presentation.
The lighting design is the same one we’ve used for years. Its has a 5-pointed wooden star mounted to the top of the porch, with a cascade of mini-lights falling from the base of the star to the fence line. It was inspired by the fact that, long ago, Stella’s father had a 5-pointed metal star that he put atop their homestead in Thorndale, TX.
In 2023, you’d think that we’d be using LED-based lights, but we’re not. They’re still quite costly. We use standard C9 lights on the star. The cascade involves 32 strands of 100-count incandescent mini-lights.
Shopping well, the old skool mini-lights can be still found for a mere $3-5 a strand. And they last several years. We never replace more than a third or half each year. While I will replace the lone damaged or burnt-out bulb, I have limited patience for testing strings that have gone completely dark.
The Schedule
In recent years, we’ve used TP-Link KASA smart outlets controlled by Home Assistant. This arrangement essentially emulates the kind of mechanical timer that might be used by less gadget obsessed folks. It simply turns the lights on/off automatically, according to a preset schedule.
Our schedule has become more involved over time. I see little reason to burn the lights continuously, all night long. So, after 1am I have them turn off. Then turn them on again an hour before sunrise, when the kids are making their way to the elementary school across the street.
I appreciate the way that Home Assistant tracks sunrise & sunset as it varies over the course of the month. This schedule not only saves power. It also prolongs the lifespan of the light strings.
Quantitative Data
Until recently we used the simpler KASA smart outlets that just turn on/off. They’re affordable and get the job done. However, for just a few dollars more there are KASA (KP115) smart outlets that also include an energy monitoring function.
These setup just like the simpler models, but exposes data about energy flowing through them. In the KASA app on my Pixel 6A I see real-time wattage and current drawn, as well as lifetime power drawn through the device. This information is also exposed to Home Assistant.
The image above is a Home Assistant display I quickly crafted. The Shelly readings (far left) are for the house as a whole. We see the star draws 258 watts (2.1A) and the cascade 883 watts (7.6A). That’s about 1,130 watts in total.
The graph above shows the power used on Thursday, November 30th. It was a warm, rainy day, so we used the furnace and/or air conditioner very little. Through midday the house hovered around its idle state, drawing just 400-500 watts. The handful of taller bars highlighted in the graph reflect periods when the holiday lights were turned on.
Also, Stella has a little electric heater under her desk that she likes to run after dinner. That explains the two slightly taller bars in the early evening.
The house used a total of 23.7 kWh that day. It’s safe to say that half of that was the holiday lights. That’s about 14 kWh. We pay around 13 cents/kWh. So the running cost of the holiday lights was about $1.82 for the day.
We started running the lights the evening of Sunday, November 26th. We’ll likely run them until Jan 2nd. That’s 38 days. So, the projected cost of power to run them would be ($1.82 x 38) around $70.
I’ll revisit this at the end of the season. It will be interesting to see the accumulated power used as tracked by the TP-Link devices.