Of all the electrical devices you have in your home, your lightbulbs probably get the most use. You’ll use them first thing in the morning, for most of the evening and they’re one of the few things in your home you would use in the middle of the night if you woke up for any reason.
So how much electricity do you use when you switch the light on? Should you be making more of an effort to switch lights off when you leave the room or is the impact minimal? And how much of a difference does the bulb type make? I’ll answer all of the questions for you now.
How much electricity does a light bulb use?
Light bulbs use very little electricity in order to work. Modern LED lightbulbs, which most homes are now upgrading to, will use somewhere between 4 and 10 watts, which is a tiny amount. Some older bulbs use a lot more, though rarely above 100 watts for residential bulbs.
Suggested read: Are LED Lights Worth It?
However, it’s important to remember that unlike some electrical devices in your home, you’ll have a lot of lightbulbs. On average, a US home has between 40 and 45 lightbulbs. It sounds like a lot but think about any lamps, or rooms with multiple fixtures – kitchens often have spotlights or under-cabinet lighting and it all adds up.
So when you’re working out the total amount of electricity that lightbulbs use in your home, you need to calculate each bulb that’s being used at any one time. It’s unlikely you’ll have all 40 switched on at once though, unless you were hosting a party and had people in every room.
What does watts mean on a light bulb?
A lightbulb’s watt rating tells you how much electricity is consumed by the bulb. A lot of people use watts as an indicator of brightness, especially to compare modern bulbs to older ones, but watts isn’t actually a measurement of brightness.
It’s strange – there is a defined measurement of how much brightness a bulb emits, which is lumens. The higher the luminosity, the brighter the bulb. But people still use watts as a rough indicator of how bright a bulb will be because they’re so used to buying incandescent bulbs that offered consistent lumens for the watts.
Where it becomes an issue is that modern bulbs use a lot fewer watts than incandescent bulbs. Unless you know that a 6-watt LED is as bright as a 60-watt incandescent bulb, or you check the lumens, then you may be a little confused on which wattage bulb you should buy.
That’s why bulb manufacturers will often advertise not just the actual wattage of the bulb, but also the watt-equivalent. An LED bulb might be marketed as being a 6-watt bulb that’s a 60-watt equivalent.
Really, we should get used to checking lumens instead of watts if we want to know how bright a bulb is, but people are used to this old way of judging brightness from the wattage, which is why the information is provided in this way.
The Different Types of Lightbulbs
There are four main types of lightbulbs that you might be using in your home. Some of these are older tech, while some are considered to be the future of lighting.
And then within those types, there are different brightness levels of bulb. There are also different bulb fixtures and bulb shapes. So you can’t really ask how many watts is a standard light bulb, as there are many, many different options!
But for the purposes of comparing power consumption, let’s take a look at those four main types of lightbulb, and then also compare a couple of different wattages of some of the more common bulb types in the US.
|Bulb Type||Average watts||Average lumens||Average lumens per watt (LPW)||Cost to run per hour ($0.14 per kWh)||Cost to run yearly (1.6 hours per day)|
This shows you how much more efficient modern LED bulbs are – they produced the same brightness as an old incandescent light but for a fraction of the cost. While a difference of around $4.30 a year might not sound a lot, remember that’s for a single bulb – multiply it by 40 bulbs and you’re talking about savings of over $150 a year.
Let’s compare some of the more common halogen and LED bulbs you can buy:
|Bulb Type||Average watts||Lumens||Lumens per watt (LPW)||Cost to run per hour ($0.14 per kWh)||Cost to run yearly (1.6 hours per day)|
|Halogen – Dim||28||370||13||$0.0039||$2.29|
|Halogen – Bright||70||1200||17||$0.0098||$5.72|
|LED – Dim||4||450||112||$0.0006||$0.32|
|LED – Bright||13||1500||115||$0.0018||$1.06|
This shows you just the scale of different bulbs – how the same types can have such different brightness levels, and how that impacts their annual energy use. If you were using bright halogen bulbs already and swapped them all for bright LEDs, you’d get brighter lights and you’d save almost $5 a year per bulb.
Incandescent bulbs have been banned
I was very careful in the last section to talk about the types of bulbs that you could be using at home, rather than the types of bulbs you can buy. And that’s because older lightbulbs – incandescent and halogen – are being phased out.
New rules in the US are making it so that any light bulb sold must provide a minimum of 45 lumens per watt, essentially ruling out the older technologies that average much lower than this.
Compact Fluorescent Lights (CFLs) are still within the permitted limits, but in reality, the move is one designed to shift everyone onto LED bulbs, which the DOE says it expects will save US consumers around $3 billion per year in total on their utility bills.
It’s worth noting that some other countries have gone a step further and announced an impending ban on fluorescent lights as well, meaning LEDs will become the only option.
How much does it cost to run a light bulb for 24 hours?
Depending on the type of bulb, it would cost somewhere between $0.20 and $0.02 to run a lightbulb constantly for 24 hours. Over the course of a year, a lightbulb left on would cost between $73 and $7.30 if it was left permanently switched on.
It’s worth noting that different bulb types also have different lifespans too – so if you were to try to run an incandescent bulb 24/7, it would likely burn out after around 40 days – they have a lifespan of between 750 and 1,000 hours on average.
LED lights last much longer – up to 50,000 hours. You could in theory leave an LED light running non-stop for between 5 and 6 years.
How to know what watt light bulb to use
To determine the best lightbulb for a room, you should calculate the footcandles required. This measurement tells you how many lumens you need per square foot. You should aim for 10-20 foot candles for bedrooms and living rooms, and 70-80 for bathrooms and kitchens.
Footcandles are useful measurements because they convert lumens into a more tangible benefit. What I mean by that is that a lightbulb producing 800 lumens will always produce 800 lumens. But if you put that same lightbulb into a tiny little room, and into a giant warehouse, it’s not going to light up the space in the same way.
Footcandles are literally lumens per square foot, and so you can measure a room and multiply it by the recommended footcandles for a space, and that’ll tell you how many lumens of light you need – and then you can use that to determine the watts of bulb required.
The watts you need are a total though – so if your kitchen has 8 spotlights, then the lumens required should be divided by those 8 bulbs.
Let’s run some examples. For simplicity, we’ll use a 10ft x 10ft room example for both.
In a bedroom, you’re recommended to have between 10 and 20 footcandles. Let’s say you rely on a single light. So you’d work out the square footage – 100 square feet – and multiply that by the footcandles. You’d then know you want between 1000 and 2000 lumens.
You could then shop for a bulb which advertizes lumens between that range, or you could work out that since LEDs generally provide between 100 and 115 lumens per watt, you want a single LED that’s between 8 and 20 watts.
For the kitchen, say you have 8 spotlights, and you want between 70 to 80 footcandles – so that’s 100 square feet x 70/80 to give you between 7000 and 8000 lumens.
Divide those by 8 spotlights and you need between 875 and 1000 lumens per bulb – so between 7 and 10 watts for LEDs.
Here’s a recommended list of footcandles in full:
|Kitchen (floor area)||30-40|
|Kitchen (worktop area)||70-80|
Individually, light bulbs don’t use a lot of electricity, especially as legislation means that we’ll all be moving to LEDs soon if you haven’t already. Using all the info here, you can easily work out which LED bulbs you need for each room in your home too.
Now, because of the move to LEDs, you might be tempted to get a little lazier when it comes to switching lights off when not in use. After all, it’s less than a cent per hour for most bulbs, right? But while it is costing you less, and they do have a long lifespan, it’s still best to stay in good habits and switch off bulbs when you’re not using them.
But just be prepared that, if you’re used to reprimanding your teenagers for leaving lights on, they may give you some backchat if they also learn these stats.