How much electricity does a light bulb use? And how much does it cost?

Turning off the lights as you leave a room is something that’s been drummed into most of us from childhood. But how much electricity does a light bulb use? And how much does it cost?

Whether it’s dark winter evenings or early mornings, our light bulbs tend to be on a lot of the time, so it’s a good idea to know how much it costs to keep the lights on. Different types of light bulb use different amounts of power, as do varying wattages.

We’ve worked out how much you can expect to spend per hour on electricity for the light bulbs in your home. We’ll also explain how to save energy at home by making the right lighting choices.

How much electricity does a light bulb use?

Many of us associate wattage with the amount of light a light bulb gives out – a dimmer 25W bulb compared with a brighter 60W bulb for example – but the wattage of a light bulb actually equates to the amount of electricity it uses. Brightness is measured in lumens.

This is why it’s common to see lower wattage bulbs described as ‘equivalent to 60W’ – it’s not the energy they require that’s equivalent, but the brightness.

The best way to work out how much energy your light bulb uses is by converting the wattage to kilowatts. So, a 100W light bulb would require 0.1kW an hour.

• Higher energy light bulbs, such as incandescent (up to 100W) and halogen (up to 120W), are being phased out. However, you may still have some of them working in your home, and you can buy decorative exposed carbon filament light bulbs that are typically 40-60W.
• CFL (or compact fluorescent lamp) light bulbs are the most common energy-saving bulb. They’re as it sounds – small fluorescent lights that typically use 60-80% less energy than an incandescent bulb yet can be up to four times more efficient. Their wattages tend to range between 6-22W.
• LED light bulbs are the most energy efficient, with typical wattages ranging from 4-18W. ‘Replacing standard bulbs with LED alternatives means you will only be using a fraction of the energy of a normal bulb,’ says Matt Manning, Group Carbon and Environment Manager at Currys. ‘Lights can be left on as needed, without the worry of a high electricity bill.’

Image credit: Future Plc/Dominic Blackmore

And how much does it cost?

According to the Energy Saving Trust the national average price (as of November 2021) per pence/kWh of electricity is 20.06p. We have rounded it to 20p for illustration purposes.

• Taking the example above, that a 100W light bulb uses 0.1kW an hour, this means that ten 100W light bulbs on at the same time would require 1kW, which would cost 20p every hour.
• Swap that for ten 18W LED light bulbs and the cost is significantly less: 18W is 0.018kW x 10 = 0.18kW, so the cost every hour is just under 4p.

‘Lighting accounts for 15% of a typical household’s electricity bill,’ reveals Steve Buckley, head of data science at energy-saving app Loop. ‘Quality LED lights cost more than other types of lighting, but it’s a price worth paying. If you replace all of the bulbs in your home with LEDs, then for an initial outlay of £100 you’ll save about £35 a year on your energy bill.’

Image credit: Future PLC/Dominic Blackmore

What energy saving features should I look for when buying a light bulb?

These handy light bulb functions and features will help you save over time.

1. Smart connectivity

Smart light bulbs that are controlled by an app, such as Hive or Hue, open up a whole world of energy saving options. These include being able to set lights to switch off at sunrise, so they’re not on longer than they need to be, to turn off all your light bulbs at once, or flick off lights in another room that have been accidentally left on.

2. Energy efficiency rating

New light bulbs are rated from A to G, with A being the most efficient, so you can see the energy efficiency at a glance. The label should also show energy consumption for 1,000 hours of use so you can easily work out how much it’ll cost to power each one. 

3. Low wattage

The lower the wattage, the less electricity a light bulb will use. Look for energy saving bulbs that provide the brightness you need (shown in lumens) with the lowest wattage possible.

Image credit: David Giles

How can I cut the cost of running a light bulb?

1. Switch to LED bulbs

‘LED lights can help reduce the average person’s carbon dioxide emissions by up to 40kg a year – the equivalent to driving a car 40 miles,’ says Matt Manning. ‘By switching from a 100W incandescent bulb to an LED light bulb, the Energy Saving Trust estimate that you can save up to £9 per bulb per year, based on a 1,100-lumen bulb running for 562 hours.’

2. Reach for the dimmer switch

While older dimmer switches didn’t save energy – adding resistance to the circuit, which was turned into heat rather than saving energy – modern dimmer switches work differently. They reduce the flow, which can also prolong the lifespan of your bulb.

However, it’s worth noting that the saving is rarely linear – for example, dimmed halogen bulbs are less efficient. Check your light bulbs are compatible before installing a dimmer switch, too – not all LEDs and CFL bulbs will be.

3. Opt for a lower wattage bulb

If you’re always reaching for the dimmer switch, consider using a lower-wattage light bulb instead. They’ll use less energy at full power than a dimmer high-wattage light bulb.

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