The Shocking Truth: How Much Electricity and Money is Actually Consumed by a Light Bulb?

From our earliest years, we are taught the simple act of switching off a light when we leave a room. As energy costs continue to skyrocket, we all become more sensitive to wasting electricity. But what is the true cost of leaving a light on? And how much is this adding to your monthly bills?

As we are all aware, energy prices rise year on year, and with the shorter days of winter approaching, our lights will soon be in constant use. The amount of electricity needed to power a light bulb depends on the type and wattage. We delved into this issue and discovered the true cost of running a light bulb in your home, as well as some invaluable strategies to save money.

How much electricity does a light bulb consume?

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It's difficult to know what uses the most electricity in your home, but understanding this can help you lower your energy usage and, in turn, your bills. Many of us assume that wattage corresponds to the amount of light emitted by a bulb - with a dim 25W bulb providing less light than a brighter 60W bulb - when, in fact, wattage represents the electricity consumed by the bulb. Brightness is quantified in lumens.

This explains why lower wattage bulbs are often described as "60W equivalents"; it doesn't mean they consume as much energy as a 60W bulb, but rather that they emit the same amount of light. To find out the amount of energy used by a light bulb, you must first convert the wattage to kilowatts. For instance, a 100W light bulb requires 0.1kW per hour.

Higher energy light bulbs, such as incandescent (up to 100W) and halogen (up to 120W), are gradually being phased out. However, your home may still have some of these light bulbs in use, and you can find decorative exposed carbon filament light bulbs that usually employ 40-60W of electricity. CFL (compact fluorescent lamp) light bulbs are the most commonly used energy-saving bulbs. They are small fluorescent lights that utilize 60-80% less energy than incandescent bulbs and can be as much as four times more effective. Their wattages typically range from 6-22W. LED light bulbs, with wattages ranging from 4-18W, are the most energy-efficient alternatives. "By substituting regular bulbs with LED alternatives," says Matt Manning, Group Carbon and Environment Manager at Currys (opens in new tab) "you will only be using a fraction of the energy of a normal bulb. Lights can be left on as needed, without the worry of a high electricity bill."

How much does it cost to power a light bulb?

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To determine the cost of running a specific light bulb, you need to know the price of electricity per kWh. As of October 2022, the national average price per kWh of electricity is 34p.

Bear in mind that the price of electricity has increased by over half since November 2021, with the figure for this period being 20p instead of 34p due to the April and October energy price cap increases.

For example, a 100W light bulb uses 0.1kW/hour, so if ten 100W light bulbs are on simultaneously, they would need 1kW, which costs 34p per hour. However, replacing them with ten 18W LED bulbs significantly reduces the cost: 18W is 0.018kW x 10 = 0.18 kW, so the cost per hour is just over 6p.

According to Steve Buckley, head of data science at Loop, “Lighting accounts for 15% of a typical household’s electricity bill.” Buckley advises choosing high-quality LED lights, which cost more but are worth the investment.

What light bulb features should I prioritize to save energy?

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To reduce the electricity consumption of your light bulbs, look for features that enhance energy efficiency, including the following:

• 1. Smart connectivity

Smart light bulbs that you can control through an app, such as Hive or Hue, provide several energy-saving options. You can program your lights to switch off at sunrise, turn off all the bulbs simultaneously, or turn off lights in any room accidentally left on.

2. Energy efficiency rating

Light bulbs are rated from A to G based on energy efficiency, so you can easily determine how efficient a bulb is. The label should also indicate the energy consumption for a thousand hours of use so you can calculate the cost of each bulb’s power consumption.

3. Low wattage

Look for energy-saving LED bulbs that have the lowest wattage possible while still providing the brightness you need (measured in lumens). The lower the wattage, the less electricity the light bulb uses.

What can I do to reduce the cost of running a light bulb?

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1. Switch to LED bulbs

According to Matt from Currys, “LED lights can help reduce the average person's carbon dioxide emissions by up to 40kg per year – the equivalent of driving a car 40 miles.”

Making the switch from a 100W incandescent light bulb to an LED light bulb can save you a considerable amount of money. According to the Energy Saving Trust, swapping to an LED light bulb allows for savings of up to £9 annually per bulb. This estimation is based on a 1,100-lumen light bulb that runs for 562 hours.

Dimmer switches have come a long way since older models which added resistance to the circuit, thereby generating heat instead of saving energy. Modern dimmer switches, on the other hand, work differently. They reduce the flow and can extend the lifespan of your bulb.

However, bear in mind, if you choose to dim halogen bulbs, you won't observe the same efficiency. It is also crucial to ensure that your light bulbs are compatible before installing a dimmer switch since not all LEDs and CFL bulbs are.

Instead of continuously relying on your dimmer switch, go for a lower-wattage light bulb. Such bulbs consume less energy than high-wattage light bulbs operating at full capacity.