What a Typical Display Costs
LED lights have made strings cheap to run: six 100-light LED strings use about 45 watts together, less than one incandescent string. In many yards today the biggest load is the inflatables. Two full-size inflatables at 100 watts each use more than four times as much as those six strings. The calculator's starting display — six LED strings, 100 LED C9 bulbs along the roofline, two inflatables and a projector — draws about 355 watts. At 6 hours a night for 40 days and 18¢ per kWh, that's about $15 for the season.
| Decoration | Watts | Per night (6 hrs) | 40-day season |
|---|---|---|---|
| 100-light LED mini string | ~7.5 | $0.01 | $0.32 |
| 100-light incandescent mini string | 40 | $0.04 | $1.73 |
| 100 LED C9 bulbs (100 ft roofline) | ~100 | $0.11 | $4.32 |
| 100 incandescent C9 bulbs | 700 | $0.76 | $30.24 |
| Small inflatable, 12 V adapter | ~18 | $0.02 | $0.78 |
| Full-size inflatable | ~100 | $0.11 | $4.32 |
| Large 10–12 ft inflatable | ~200 | $0.22 | $8.64 |
At 18¢ per kWh. EnergySage's December example lands in the same range: a 6-foot tree, wreath, two lawn ornaments and 500 feet of roofline C9s cost about $131 with incandescent bulbs and about $20 with LEDs at 6 hours a day.
Old C9 Bulbs Are the Expensive Part
Classic incandescent C7 and C9 bulbs are the one decoration that can move a power bill. At 7 watts per bulb, 500 feet of C9s on 12-inch spacing draws 3,500 watts — more than two space heaters. Running 6 hours a night for 40 days, that's about $150 of electricity. The same roofline in LED C9s draws about 480 watts and costs about $21. If you still have incandescent big bulbs, swapping them pays back faster than any other holiday change.
The Department of Energy's older comparison makes the same point for a 6-foot tree lit 12 hours a day for 40 days: about $25 with C7 incandescent bulbs, $6 with mini incandescents and 56¢ with LEDs, at the 10.5¢ per kWh rates of the time.
Timers Cut the Bill in Half
Lights left on dusk to dawn run 14 hours or more in December. A timer or smart plug that shuts them off at midnight runs them about 6 hours, so it cuts the display's cost by more than half. It also keeps the outdoor plugs from running all night in rain and snow. Use outdoor-rated timers and cords, and plug outdoor decorations into GFCI-protected outlets.
Why the December Bill Still Jumps
If your December bill is up $40 or $80, lights are rarely the main reason unless you run a big incandescent display. Shorter days, more heating, holiday cooking, guests and space heaters usually add far more. Our electric bill spike calculator sorts out how much of an increase comes from weather and season versus everything else.