Holiday String Lights Energy Cost Calculator

Energy cost formula for string lights

The calculator uses a straightforward energy formula that converts watts and hours into kilowatt-hours, then multiplies by your electricity rate. In words, the cost equals:

Cost = Number of strings × Wattage per string × Hours per day × Days used ÷ 1000 × Electricity rate

In symbolic form:

Where:

• C = total seasonal cost of running the lights (in dollars)
• N = number of light strings
• W = wattage per string (in watts)
• H = hours the lights are on each day
• D = number of days you use the lights
• R = electricity rate (dollars per kilowatt-hour, $/kWh)

The division by 1000 converts watt-hours to kilowatt-hours, since utilities bill in kWh. The same formula applies to both incandescent and LED strings; the key difference is the W value you use.

Example: seasonal cost for a typical display

Consider an example with a moderate holiday display:

• 10 incandescent strings
• 40 W per string
• 6 hours per day
• 45 days of use
• Electricity rate: $0.16/kWh

First calculate total energy use:

Energy (kWh) = 10 × 40 × 6 × 45 ÷ 1000

Multiply the numbers in the numerator:

• 10 × 40 = 400 W of lights
• 400 × 6 = 2,400 watt-hours per day
• 2,400 × 45 = 108,000 watt-hours for the season

Convert watt-hours to kilowatt-hours:

108,000 Wh ÷ 1000 = 108 kWh

Now multiply by the electricity rate:

Cost = 108 kWh × $0.16/kWh = $17.28 for the season.

For the LED comparison, assume the same number of strings but with an average of 5 W per LED string:

• 10 LED strings
• 5 W per string
• 6 hours per day
• 45 days of use
• Electricity rate: $0.16/kWh

Energy (kWh) = 10 × 5 × 6 × 45 ÷ 1000

• 10 × 5 = 50 W of lights
• 50 × 6 = 300 watt-hours per day
• 300 × 45 = 13,500 watt-hours per season

Convert to kWh:

13,500 Wh ÷ 1000 = 13.5 kWh

Cost = 13.5 kWh × $0.16/kWh = $2.16 for the season.

In this scenario, switching to LEDs cuts your seasonal lighting cost from $17.28 to $2.16, saving more than $15 in just one holiday season.

Incandescent vs. LED holiday lights: comparison table

The table below summarizes the example above and shows how runtime affects energy use and cost for the same display. It uses:

• 10 strings
• 40 W for each incandescent string
• 5 W for each LED string
• 45 days of use
• Electricity rate of $0.16/kWh

Use this as a quick reference to see how strongly both light type and hours per day affect your bill. Then plug your own numbers into the calculator to get personalized results for your home or display.

Interpreting your results

When you run the calculator with your own values, you will see the total seasonal energy use and cost for the setup you entered. Here are some ways to interpret the numbers:

• Daily cost perspective – Divide the seasonal cost by the number of days used to see the approximate cost per day. This can make even a larger seasonal total feel more manageable.
• Budget planning – Add the seasonal cost from your lights to other expected holiday expenses to avoid surprises on your January electricity bill.
• Upgrade decisions – Compare the incandescent and LED scenarios. If the savings from LEDs over just one or two seasons are close to the price of new strings, upgrading can quickly pay for itself.
• Runtime trade-offs – Try different “hours per day” values. You might find that trimming just one or two hours per night has a meaningful impact on cost, especially for larger displays.

Remember that this calculator focuses on the electricity used directly by your decorative lights. It does not account for any indirect effects, such as indoor lights slightly warming a room or outdoor lights affecting your heating or cooling usage.

Assumptions and limitations

All calculators simplify reality to make planning easier. To interpret your results correctly, keep these assumptions and limitations in mind:

• LED comparison wattage – For the LED savings scenario, a typical value of about 5 W per string is assumed. Actual LED strings can use more or less power depending on bulb count, spacing, brightness, and special effects (such as chasing patterns or color changes). Check your product label for a more precise figure.
• Wattage input accuracy – The results are only as accurate as the wattage you enter. Use the wattage printed on the box, on the tag near the plug, or in the product manual. If you guess, your energy and cost estimates will also be approximate.
• Electricity rate – The tool uses the single $/kWh rate you enter. It does not model taxes, fixed service charges, time-of-use pricing, or tiered rates that change after a certain usage level. For most people, using the main rate shown on the bill provides a good estimate.
• Constant daily schedule – The calculator assumes the same number of hours per day and days of use throughout the season. If you run lights longer on weekends than weekdays, you can either enter an average value or run two scenarios and add the results.
• Indoor vs. outdoor use – The electrical energy use is the same whether the lights are indoors or outdoors. This tool does not model any effect on heating or cooling loads.
• No other devices included – The calculation applies only to the light strings themselves, not to inflatables, projectors, music controllers, or other decorations you might plug in.

Because of these simplifications, think of the output as a solid estimate rather than a guaranteed exact bill impact. For most households and community displays, this level of detail is more than enough for planning and comparison.

Tips to reduce holiday lighting energy use

If the cost estimate is higher than you expected, you can often lower it substantially without giving up the festive look. Consider the following strategies:

• Switch to LED strings – Replacing old incandescent strings with LED versions is usually the single biggest energy saver, often reducing electricity use by 70–90% for the same visual effect.
• Use timers or smart plugs – Set your lights to turn on at dusk and off at a specific time instead of running all night. This keeps your display visible when people are awake while trimming late-night hours that few notice.
• Focus on high-impact areas – Concentrate lights on entryways, windows, railings, and trees where they are most visible, rather than trying to cover every surface.
• Dim or simple effects – Some LED systems allow you to choose dimmer settings or simple steady-on modes that may use slightly less power than complex, bright animations.
• Test small changes in the calculator – Use the tool to see how your cost changes if you reduce runtime by an hour or remove a few strings. Small adjustments can add up over a month-long season.

Frequently asked questions

How many watts does a typical string of holiday lights use?

Incandescent mini-light strings often use around 35–70 W per string, depending on the number of bulbs. Larger C7 or C9 incandescent bulbs can draw much more. Comparable LED strings that provide a similar amount of light commonly use about 3–8 W per string. Always check your specific product label for the most accurate wattage.

Where can I find my electricity rate?

Look at your latest electricity bill for a line labeled “Rate,” “Energy charge,” or something similar, usually given in cents or dollars per kWh. If your bill lists multiple rates (for example, on-peak and off-peak), use a typical or weighted-average rate to get a reasonable estimate with this calculator.

How much can I save by switching to LED holiday lights?

Savings depend on how many lights you have, how long you run them, and your local electricity rate. In many cases, LEDs can cut holiday lighting energy use by 70–90% compared with older incandescent strings. If you have a large display or run it for many hours each night, the dollar savings can be significant over just a few seasons.

Does it matter if my lights are indoors or outdoors?

From an electricity-use standpoint, a 40 W string uses the same amount of energy regardless of where it is installed. This calculator focuses only on the electrical cost. It does not include any small side effects on your home’s heating or cooling system.

Why does the calculator ask for days and hours separately?

Separating hours per day and days of use makes it easier to think about your real schedule. Many people run lights only for part of the evening, and only for a portion of the season. Entering both values helps you get a more accurate seasonal total instead of just a daily snapshot.

How this calculator is different

Unlike generic energy calculators that treat every device the same, this tool is tailored to decorative holiday lighting. It focuses on variables you can control—how many strings you use, how bright they are, how long you run them, and whether they are incandescent or LED. By experimenting with these inputs, you can design a display that fits both your aesthetic goals and your energy budget, making the season bright without overspending on electricity.