(NEXSTAR) – Whether you’re wrapping your Christmas tree in one strand of lights or adorning your home with a Griswold-like display, the type of lights you select can have a big impact on your electric bill.

A walk down the aisle of Christmas lights can be overwhelming. First, the bulb type – LED or incandescent? Then there’s the size of the bulb, with the most common ranging from the typical strand of mini bulbs, followed by C7 and the larger C9 (roughly 2.25″).

First, the math. Electricity usage is charged by the kilowatt-hour and lights carry a certain wattage. To determine the electricity usage of a strand of lights, follow this formula:

1. Multiply wattage by the hours per day the lights will be on, then divide by 1,000 to find kilowatt hours, or kWh per day.
2. Multiply the kWh per day by your cost of power usage (found on your electric bill) to find the cost per day.
3. Multiply the cost per day by how many days your lights will be on.

The latest data from the U.S. Energy Information Administration shows the national average price for electricity for customers in September 2022 was a little more than 16 cents per kilowatt-hour. That rate varies, with those in Alaska, California, Hawaii, and New England seeing higher-than-average costs.

Now, the comparisons. Three different styles of light strands — mini, C9, and C7 — are compared below, based on whether the bulbs are LED or incandescent. For these comparisons, each cost was based on six hours of usage per day, over 30 days.

A strand of 300 white mini LED lights on the typical green wire is 21 watts, while the same style with incandescent bulbs is 72 watts. Using the formula above with the national average of 16 cents per kilowatt-hour and a display season of six hours a day for a month, using a strand of mini LED lights will cost you about 60 cents. A strand with the same amount of incandescent bulbs will cost about \$2.07.

If you’re looking at a strand of 100-light C9 LED lights at 4.8 watts, it will cost you about 14 cents, while a 25-light strand of C9 incandescent lights at 175 watts costs about \$5.04. For the 25-light LED C7 strand at 21 watts, your cost is about 60 cents, while the incandescents at 125 watts will cost about \$3.60.

Of course the total cost is dependent on the local cost of electricity. In Idaho, which had the lowest average price of electricity in September at about 10 cents, the costs above would range between 9 cents and \$3.15. In Hawaii, with the highest average price of nearly 46 cents, costs would range between 39 cents and \$14.18.

While LED light strands tend to cost more at the store — those referenced above range from about \$30 to \$80 compared to the incandescent strands ranging between \$9 and \$22 — incandescent will put a greater strain on your electric bill over time.