ElectricalToolbox

Are LED Halloween Lights Cheaper to Run Than Incandescent?

Yes, and it is not close. A string of LED Halloween lights draws roughly a tenth to a fiftieth of the power of the same-size incandescent string. Over a full October that is the difference between a few cents and a few dollars per string, so a big display saves real money. But the bigger win is safety: because LEDs pull so little current, you can connect far more of them before you overload a circuit, and they never get hot enough to scorch a cord or a plug the way incandescent strings can.

Planning how much of a display one outlet can carry? Total the wattage on your light boxes, divide by 120 to get amps, and check it against the circuit with the Extension Cord Voltage Drop Calculator. Switching to LED changes that math completely.

Where the savings come from

An incandescent bulb makes light by heating a metal filament until it glows, and most of the energy it uses leaves as heat, not light. An LED makes light directly and stays cool to the touch, so for the same brightness it needs a fraction of the power. That single fact drives three things at once: a lower power bill, a much lighter load on your wiring, and far less heat sitting against the cord. The savings are real, but the load and heat differences are what actually keep a display safe.

Worked example: what a season actually costs

Take a common 25-count C9 string. In incandescent bulbs that is about 7 watts per bulb, so 175 watts for the string. The LED version of the same 25-count C9 string draws around 4 watts. Run either one 6 hours a night for the 31 nights of October, which is 186 hours, at the U.S. average home electricity rate:

Incandescent: 175 W × 186 h = 32.6 kWh × $0.17 = about $5.53

LED: 4 W × 186 h = 0.74 kWh × $0.17 = about $0.13

Per string, per season: about $5.50 vs about 13 cents

The rate used here is about 17 cents per kilowatt-hour, close to the recent U.S. residential average; your own rate is printed on your power bill, so swap it in if it differs. One string barely matters either way. Multiply by the twenty or thirty strings on a real display and the incandescent version costs well over a hundred dollars for the month while the LED version costs a few dollars.

The safety difference: how many you can run

The cheaper power bill is nice. The reason an electrician cares is the load. A standard 15-amp household circuit should carry no more than 80 percent of its rating on anything left running for hours, which is 12 amps, or about 1,440 watts at 120 volts. Watts divided by volts gives the amps each string pulls:

Incandescent C9: 175 W ÷ 120 V = 1.46 amps per string

1,440 W budget ÷ 175 W = about 8 incandescent strings before the circuit is full

LED C9: 4 W ÷ 120 V = 0.03 amps per string

1,440 W budget ÷ 4 W = hundreds of strings before the circuit is the limit

With incandescent strings you run out of circuit after about eight sets. With LEDs the circuit stops being the thing that limits you. What limits you instead is the manufacturer's maximum number of sets you are allowed to connect end to end, which is set by the small fuse in the plug and the wire in the string, not by your breaker. That limit is printed on the box, and it still applies no matter how little power the lights use. See how many light strings you can connect end to end for that side of it.

To size the whole display against your outlet, add up every box's wattage and run it through the extension cord voltage drop calculator, or walk through the load step by step in the guide on how many amps of decorations one cord can carry.

Cooler cords, fewer fires

Incandescent strings do not just cost more to run, they put heat into everything they touch: the bulbs, the string wire, and the extension cord feeding them. A filament bulb turns most of its energy into heat, so the glass gets hot enough to be a burn or ignition risk against dry leaves, cornstalks, fabric, or a coiled cord, and that stacked-up heat is one of the ordinary ways a holiday display starts a fire. LEDs stay cool to the touch, draw a tiny fraction of the current, and take that heat out of the picture, which is why they are the safer choice as much as the cheaper one.

Switching does not make the outdoor rules go away

LEDs cut the load and the heat, but they do not change the fact that anything outside has to survive weather. The lights and cords still need to be outdoor-rated, everything plugged in outside still needs GFCI protection, and the connections still have to be kept out of the water. Lower wattage often means you can use fewer and shorter cords, which leaves fewer connections to weatherproof, but it does not remove the need. See whether Halloween lights can get rained on for how to protect the connections. If a display or a circuit is not behaving the way you expect, stop and call a licensed electrician rather than guess.

NEC reference

National Electrical Code (NEC) 2020. The 80 percent ceiling on a continuous load, the rule behind the roughly 12-amp usable budget on a 15-amp circuit, comes from NEC 210.19(A) and 210.20(A). Extension cords and light-string cords are flexible cord under NEC Article 400. The wattage figures here are typical published values for common C9 strings, not code table values, so the numbers printed on your own light boxes are what govern the count.

Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.

Get the full guide

NEC Code Quickstart

This guide covers one calculation. NEC Code Quickstart walks all twelve exam calculations start to finish, each with a worked example and the exact code reference: ampacity and derating, breaker sizing, voltage drop, box and conduit fill, grounding, dwelling load, range and dryer demand, motor circuits, and transformer current. Written for the 2023 NEC with notes for the 2026 edition.

Read on Kindle Paperback on Amazon

Related