The Running-Cost Math

How Much Electricity Do Christmas Lights Use?

By the North Texas Christmas Light Installation team · October 2026 · Sources: U.S. Energy Information Administration (Electric Power Monthly, July 2026 data); U.S. Department of Energy; U.S. Consumer Product Safety Commission; ERCOT; manufacturer and retailer spec listings

Every December someone looks at a lit roofline and wonders what the meter is doing. For LED, the answer is: very little. Here is the arithmetic with every input sourced, so you can redo it for your own roofline and your own electricity plan.

The formula

Electricity is billed in kilowatt-hours (kWh). One formula covers any light display:

Total watts × hours of use ÷ 1,000 = kWh. Then kWh × your rate = cost.

Worked once, for 150 typical C9 LED bulbs: 150 bulbs × 0.8 W = 120 W. Six hours a night for 45 nights is 270 hours. 120 W × 270 h ÷ 1,000 = 32.4 kWh. At $0.1588 per kWh, that is $5.15. That's the season, not the month.

The inputs, and where they come from

• LED C9 bulb: about 0.8 watts. A typical commercial-grade C9 LED retrofit bulb is listed at under one watt. The example used here is an OptiCore C9 LED retrofit bulb, listed at 0.8 watts per bulb on an E17 base (christmaslightsetc.com spec listing, checked October 2026). Other bulbs vary, so read the listing for the ones you're pricing.
• Incandescent C9 bulb: 7 watts. The traditional glass C9 replacement bulb is a 7-watt, E17-base lamp (1000bulbs.com spec listing, checked October 2026).
• Spacing: 12 inches. Bulk C9 socket wire is commonly sold with sockets every 12 inches — a 1,000-foot spool carries 1,000 sockets (Seasonal Source and Novelty Lights spool listings, checked October 2026). So feet of roofline is a fair stand-in for bulb count.
• Electricity price: 15.88¢ per kWh. That is the average residential price in Texas for July 2026, the most recent month in the U.S. Energy Information Administration's Electric Power Monthly (Table 5.6.A) when we checked in October 2026. The U.S. average for the same month was 18.31¢.
• Schedule: 6 hours a night for 45 nights. Roughly dusk to bedtime from before Thanksgiving into early January. This one is our assumption, not a statistic — change it to match your habits.

Three rooflines, both technologies

Assumptions: one bulb per foot (12-inch socket spacing); 0.8 W per typical C9 LED bulb and 7 W per incandescent C9 bulb, per the spec listings above; 6 hours a night for 45 nights (270 hours); 15.88¢/kWh, the Texas average residential price for July 2026 (U.S. EIA, Electric Power Monthly). Energy charges only — a plan's fixed monthly fees don't change with the lights. Rounded to the cent.

The ratio never moves: 7 ÷ 0.8 = 8.75. Whatever the roofline, schedule, or rate, an incandescent C9 costs 8.75 times what this LED bulb does to run — put the other way, the LED uses about 89% less energy in the same row of sockets. Not sure of your footage? The roofline estimator will get you close in a minute.

A cross-check from the Department of Energy

The U.S. Department of Energy's own holiday-lights explainer says LED strands consume 70 percent less energy than conventional incandescent strands, and gives an example: about $0.27 to light a six-foot tree 12 hours a day for 40 days with LEDs, against $10 with incandescent (energy.gov, "How Do Holiday Lights Work?", December 2015). Different product, older rates, same conclusion. The C9 gap is wider than DOE's general figure because the incandescent C9 is a particularly thirsty bulb.

Durability points the same direction. The LED bulb in our example carries a 60,000-hour rating; the incandescent C9 listing gives an average rated life of 3,000 hours. Rated hours are bench numbers, not a promise about a Texas roofline in December, but a twenty-to-one ratio tells you which technology is the consumable.

Your rate is not the average

15.88¢ is a statewide average across every utility and plan. Yours is probably different. Much of DFW sits in Texas's competitive retail market — ERCOT says it administers retail switching for 8 million premises in competitive choice areas — where you choose a retail electric provider and a plan, and the Public Utility Commission of Texas runs powertochoose.org for comparing offers. Other North Texas homes are served by an electric cooperative or a city-owned utility that sets its own rates; CoServ, for one, describes its territory as part of the share of the state exempt from that system (coserv.com, checked October 2026).

Either way, the fix is the same: find the energy rate on your bill and substitute it. A 150-foot LED roofline is 32.4 kWh for the season, so at 12¢ it costs $3.89 and at 20¢ it costs $6.48. Within that range, no plan turns this into a large number.

Circuits: why LED fits where incandescent didn't

Watts also decide how much lighting one cord and one outlet can carry. Every wire has a rating, and incandescent C9 used it up fast.

A concrete example: Novelty Lights lists its 8-amp C9 socket wire (SPT-1, 12-inch spacing) at 960 watts, with a maximum run of 137 sockets using 7-watt incandescent bulbs and 384 sockets using 1-watt LED bulbs (noveltylights.com spec listing, checked October 2026). At a bulb per foot, 137 sockets doesn't reach the end of a 150-foot roofline — 150 incandescent bulbs is 1,050 watts, over that wire's rating. So an incandescent roofline that size had to be split into separately fed runs. The same 150 sockets with 0.8-watt LED bulbs draw 120 watts.

That's one retailer's published limit for one product. The rating that governs your display is the one printed on your own socket wire, cords, and breaker — read them before connecting runs together.

Two points from the U.S. Consumer Product Safety Commission's holiday decorating guidance apply to any outdoor display, LED or not: use only lights tested for safety by a nationally recognized testing laboratory, with outdoor sets labeled for outdoor use, and plug them only into a ground-fault circuit interrupter (GFCI)-protected receptacle or a portable GFCI. The CPSC also says to check every set, new or old, for broken or cracked sockets, frayed or bare wires, and loose connections (CPSC holiday safety releases, December 2008 and December 2017).

Timers: worth having, but not for the money

A timer cuts hours, and hours are one of the three numbers in the formula. Run the 150-foot LED roofline 12 hours a night instead of 6 and the season costs $10.29 instead of $5.15. The timer saves $5.15. Each hour you trim from the nightly schedule is worth about 86 cents over the whole season.

With incandescent the same timer mattered: $90.04 against $45.02. With LED it is a convenience — the lights come on at dusk without anyone remembering. The CPSC's standing advice is to turn off all holiday lights when you go to bed or leave the house, and a timer is the easy way to follow it.

What actually costs money in a professional display

Not the electricity. Published DFW market data puts full-service C9 LED installation at $5–$12 per linear foot, with most DFW homes landing between $700 and $2,500+. That is market data, not our price list. For a 150-foot roofline that per-foot range works out to $750–$1,800, against about $5 of power: well under one percent of the total.

What you're paying for is labor at height, commercial-grade materials cut to fit, in-season repair visits, January takedown, and storage. The DFW cost guide breaks those down. If a quote ever leans on "energy savings" as a selling point for LED, the saving is real — it's just forty dollars, not four hundred.