What Christmas lights cost

Decorative lights stay on for weeks, often for many hours a day, and there can be hundreds or thousands of them. A single light uses a tiny amount of power, but multiplied by the number of lights, the hours and the days of the season it becomes a visible item on the bill, especially with old incandescent bulbs. This calculator estimates the energy and cost of the season and tells you how much you would save with an LED set and how many seasons it would take to pay for itself.

It works in any currency, for indoor and outdoor lights.

How the calculation works

• Total power: number of lights × watts per light. If you only know the set's power, divide it by the number of lights.
• Season energy: total power × hours a day × days, divided by 1000 to get kWh.
• Cost: kWh × energy price.
• LED comparison: the same calculation with the watts per light of an equivalent LED set; the set price divided by the saving gives the payback in seasons.

The verdict is based on the season's kWh, which do not depend on the currency.

The type of light makes the difference

Indicative power per light, 6 hours a day for 40 days, energy at 0.30 per kWh:

Real values vary from product to product: check the power shown on your set's label or power supply. Switching to LEDs cuts consumption by about 80-90%.

How much the hours on matter

With 500 incandescent mini lights at 0.4 W for 40 days:

A timer or programmable plug that switches the lights off at night is the simplest way to cut consumption, whatever lights you use.

Is a new LED set worth buying?

It depends on how much your current lights use and how often you use them. Replacing heavily used incandescent lights often pays for itself in a few seasons; replacing sets that are already LED saves nothing. If your old lights work and are rarely on, using them until they wear out may be the cheapest choice. LEDs also run cooler, an advantage on trees and decorations.

The bands of the verdict

• Below 5 kWh: negligible use.
• 5 to 25 kWh: modest use.
• 25 to 100 kWh: use you will notice on the bill.
• Above 100 kWh: high use; it is worth cutting the hours or switching to LEDs.

Safety

Use lights rated for outdoor use when you put them outside, do not connect more strings in series than the manufacturer allows, and switch decorations off when you go out or go to bed. Check cables and bulbs for damage before putting them up.

Limits of the calculator

The calculation uses the rated power and does not include the standby draw of power supplies and timers, or light effects that change the power while on. For battery lights the cost depends on the batteries, not mains electricity. Time-of-use energy prices can change the result.

Frequently asked questions

How much electricity do Christmas lights use?

It depends on type, number and hours on. 500 incandescent mini lights at 0.4 W on 6 hours a day for 40 days use about 48 kWh; the LED version about 8 kWh.

What do Christmas lights add to the bill?

With energy at 0.30 per kWh, the example above costs about 14.40 a season with incandescent lights and about 2.50 with LEDs.

How much do LED lights save?

Usually 80-90% of the energy compared with incandescent bulbs, because each LED draws a fraction of the power.

How do I find the wattage of my lights?

On the set's label or power supply. If the total power is shown, divide it by the number of lights to get watts per light.

Is it worth replacing old lights?

If they are incandescent and on for many hours, an LED set often pays for itself in a few seasons. If you use them little, keeping them while they work may cost less.

How many hours should I keep them on?

As many as you need to enjoy them: switching them off at night with a timer cuts consumption a lot without losing any of the effect.

Do battery lights use electricity?

Not from the mains, but they use batteries: their cost depends on battery price and life.

Are LEDs safer?

They run much cooler than incandescent bulbs, an advantage on trees and decorations. They should still be used as the manufacturer directs.

Do flashing effects use more?

Usually not: light effects switch parts of the string off in turn, so average consumption can be slightly below the rated power.

Does the calculator include the power supply?

No: the small standby draw of power supplies and timers is not included.

Can I use it for year-round decorative lights?

Yes: enter the real hours and days they are on.

Does it work in any currency?

Yes. Enter the energy price in your currency; the verdict is based on kWh, which do not depend on the currency.