The Ultimate Beginner’s Guide to Energy Saving Light Bulbs

Ultimate beginners guide to energy saving light bulbs

This guide is intended to provide general guidance only. It is not intended to give you advice on your personal financial circumstances. You should seek independent professional advice if you’re unsure about anything mentioned in this guide or what choices to make.

Five years ago I bought my first LED light bulbs. They were to replace halogens in my bathroom. I spent too much money on not enough lumens and way too many kelvin. You know what I mean?

No? Perfect. Let's make a deal.

If you spend ten minutes reading this post, I promise you that by the end of it you'll understand how to buy a low energy light bulb. In return, I'll try not to bore you senseless.

Ready? Let's do this. With five simple questions.

1) What fitting do you need?

This is simple, but you really don't want to mess it up.

Although there are literally hundreds of light fittings in existence, your home probably only has a couple. I've got two in my ceiling fittings, a couple more in table lamps. In the image below there are some common ones for the UK and US.

Bulb fitting

'B' is for Bayonett - it's a bit of a British Empire thing. 'E' is for Edison Screw, dominant in the US thanks to Thomas.

You don't need to know what they mean. But if you scribble down the fittings before you start shopping for bulbs, not only will they fit, they'll be the right voltage too.

2) What shape bulb do you want?

Bulb shape is not just a question of liking the look of a bulb: it is about how it throws light. The design of the bulb determines what direction the light goes, so you need to consider what you want the bulb to do.

common lightbulb shapes

There’s an encyclopedia of different bulb shapes, but since I promised not to bore you, I'm not going to go there. All you need to do for shape is use your common sense.

For a ceiling pendant you might want an 'omnidirectional' bulb like the arbitrary, stick or spiral shape. For a lamp, you might need a candle shape with a broad spread. And if you are putting a spot into a recessed downlight, you'll need a reflector with an appropriate beam width for the context.

A bulb that throws the wrong angle light can be really annoying, so do take the time to contemplate the shape before you buy.

3) How bright does it need to be?

It is no longer enough to think about bulb brightness in terms of watts. That was fine when we only had incandescents, but now we need to start thinking in lumens.

This is particularly the case when buying LEDs, because the use of the term 'replacement' can be abused by bulb re-sellers, and occasionally by lesser manufacturers too. The following tables are a rough explanation of how many lumens you get from your watts, for different bulb technologies for a standard fitting.

I had to make two charts to explain this properly. One for our readers in the low voltage (120V) countries like the US, Canada, Brazil and Japan. And a second one for readers in high voltage (240V) countries - that's the rest of the world.

The American Lumen:

If you live in the US, or anywhere else with a lower voltage grid, please look at this first chart. If you live elsewhere skip straight to the second.

the american lumen

At the top of this chart you have the brightness of the bulb in lumens. This is the number you need to start thinking in.

Let's say you're in the US and want to replace an old 60W bulb and get a similar amount of light. Then you know you'll need to get at least 800 lumens in order to match the brightness of the old 60W .

Got it? If you know your lumens, you won't be mis-sold a 'replacement bulb' that isn't bright enough.

The British Lumen:

In the rest of the world we have higher voltage, meaning that lumen equivalent for standard incandescents is different. That's the case here in the UK.

how many lumens do you need?

At the top of this chart you have the brightness of the bulb in lumens. This is the number you need to start thinking in.

Let's say you're in the UK and want to replace an old 60W bulb and get a similar amount of light. Then you know you'll need to get at least 700 lumens to get a similar brightness to the old bulb.

Knowing your lumens means you will get the brightness you want, and avoid being mis-sold 'replacement bulbs'.

A quick word on spotlights:

The charts above are designed to help you replace a normal lightbulb. When it comes to spotlights you can often experiment with going for fewer lumens. In our bathrooms I have replaced 700lm halogens with 320lm LEDs and actually prefer the light. The result is a 90% energy use reduction per bulb.

4) Do you want warm or cold light?

This question might sound complicated, but it's one of the great things about LEDs.

The temperature of light can be measured in terms of 'kelvin'. Very orange light has a low number of kelvin - for example, a candle is about 1,500K. Daylight is much colder, often above 5,000K. Here is the scale.

light temperature

When it comes to household light bulbs the temperature choices are very simple. Most people simply want what is called 'warm white' (2,700K) to replicate the warm, slightly yellow glow of an old incandescent or halogen.

In a kitchen, bathroom or other situations you may prefer a slightly less yellow light, sometimes called a natural white (3,000K). You may want to try cool white (4,000K). Or for a very specific style, something nearer 5,000K. Anything above that starts to get a little blue.

This type of temperature choice is mostly associated with LEDs. If your home has a quite modern, you should definitely consider trying some cooler temperatures, as they can look great in the right context.

5) Are LEDs good value yet?

Compact fluorescent (CFLs) bulbs are now so cheap that a CFL can pay itself off with energy savings in just months for a well used bulb. I personally like CFLs in the right context, but if you want instant light, dimming or cooler light, they aren't great.

LEDs on the other hand, are gradually overcoming many of these problems. The main issue with LEDs at this point is their upfront cost. This is particularly true for 75W and 100W replacements (I'm waiting for prices to drop).

With this in mind, let's crunch some numbers and see how the payback is for LEDs. In the following chart, I estimate how quickly energy savings will recoup the cost of replacing a 60W incandescent with a 10W LED that costs £6, assuming the bulb is used for two hours each day.

LED payback time around the world

Because of the huge difference in the prices of electricity, the £6 outlay for the LED pays itself off in anything from 9 months in expensive Denmark to three and a half years in India or China, where electricity is cheap.

Now a 60W LED for £6 is still quite cheap. If you are paying closer to £9, you'd need to add 50% to these payoff times. On the other hand if you are using the bulb four hours a day, then you should halve them. What does this mean for you in practical terms?

  • Cheaper LEDs payback faster
  • Payback is faster where electricity is expensive (the UK)
  • The more you use a bulb the faster the payback
  • Replacing CFLs with LEDs is not yet cost effective

In most cases, the one - year running cost of an incandescent bulb you use regularly (>two hours a day) is greater than any drop in LED prices we are likely to see. So it makes sense to switch when you see a decent value bulb. However, if you don't use a bulb much (< one hour a day) you may want to wait for prices to fall a little more. Especially for 100W replacements which are still extortionate.

I have one incandescent left in my loft that I'd be lucky to use for ten hours a year. I'll probably only switch it if it blows.

5 Steps to Buying an Energy Saving Light Bulb

If you've made it this far, you now know a lot about light bulbs. Because I promised not to bore you, I've decided to skim over dimming (read the labels), color rendering (above 80 please) and bulb lifespan (buy a known brand).

Let's just recap the five steps:

  1. Fitting: Write down the code
  2. Shape: Decide on the best shape
  3. Brightness: Get enough lumens!
  4. Temperature: Warm or cool?
  5. Cost: Look for good value-bulbs

Like I said in the introduction, I bought my first LED five years ago and only really got the first of these five steps correct. But things have changed an awful lot in five years, and LEDs are now becoming a really sensible option. CFLs remain excellent value due to their low prices and running costs, but you can't always get the light you want.

If you have never bought LEDs before, I highly recommend trialling a single bulb, or spotlight first - before buying too many. LEDs are not cheap and last a long time, so you want to be sure about fitting, shape, lumens and kelvins before going all in on them. I also recommend looking for specials on known brands or having a money - back guarantee up your sleeve.

Good luck with your LED hunt and I hope you get the right fit, shape, brightness and temperature at a decent price. Most importantly, I hope you prefer the light of your new bulb - that's the main test of success.

This article is by Lindsay Wilson from

Find out how much you could save by changing your light bulbs with our lightbulb cost calculator

*Source and notes for graphs and table

How many lumens do you need? (120V)


How many Lumens do you need? (240V)

Sources: European Commission

Light Temperature in degrees Kelvin


LED payback times around the world (years)

Sources: IEA - Assumptions: this analysis assumes a 60W incadescent is replaced with 10W LED that costs $10 and that the bulb is used for 2 hours each day. No additional bulb costs are assumed. Increasing bulb cost will increase paypback time, increasing bulb use will reduce it.

Read more Read less

O​VO​ Energy Ltd, registered office 1 Rivergate Temple Quay Bristol, BS1 6ED, company no. 06890795 registered in England and Wales, VAT No. 100119879

Additional terms and conditions
Please see below for full terms and conditions on 33% renewable electricity, 3% interest rewards, exit fees and saving claims.


1Monthly cost - Representative monthly direct debit costs based on a non-economy-7, dual-fuel, medium user (3100 kWhs elec. and 12500 kWhs gas) paying in advance by direct debit, including online discount.  All rates correct as of 22/11/2017, but may go up or down.

2Weekly cost - Representative weekly costs based on a non-economy-7, dual-fuel, medium user (3100 kWhs elec. and 12500 kWhs gas).  All rates correct as of 22/11/2017, but may go up or down.

3Pay Monthly Savings claims: Saving based on the estimated annual cost of OVO Two year fixed tariff for a non-economy-7, dual-fuel, medium user (3100 kWhs elec. and 12500 kWhs gas) paying monthly in advance by direct debit, including online discount. Comparisons made against the average of the Big 6 standard variable tariffs with equivalent features. All rates correct as of 22/11/2017.“The Big 6” are British Gas, Scottish Power, SSE, Npower, E.ON and EDF.

4Pay As You Go Savings are based on the average estimated annual costs for new PAYG OVO customers quoted through the OVO website (based on household and/or consumption information provided by those customers), compared to their current supplier and tariff. Comparisons taken between 01/01/2016 and 11/10/16. Incl VAT. Actual savings may vary according to your current supplier or tariff, individual tariff options, household information, consumption and location. 

We include almost twice as much renewable electricity as the national average: At least 33% of electricity in all of our tariffs comes from renewable sources. The national average, according to Ofgem as at March 2014 was 16.7%. For more information please visit this page.

33% of your electricity comes from renewable sources: 33% renewable electricity as standard as of 1st April 2015. Renewable electricity is generated from wind, solar, geothermal, wave, tidal, hydro, biomass, landfill gas, sewage treatment plant gas and biogas.

3% interest: Calculated at 3% per year for customers paying by advance direct debit.  The OVO Interest Reward is paid monthly based on   number of days in credit and the amount left in your account after you’ve paid your bill,  and the credit balance on which you can earn the OVO Interest Reward is capped. Terms apply:

95% of new customers save when switching to OVO: Savings based on the average estimated annual costs for all new OVO customers quoted through the OVO website, compared to their current supplier and tariff. Comparisons taken between 01/05/2016 and 11/10/16. Incl VAT.

94% of surveyed customers would recommend us: OVO conducted a survey of their customers in between 1st January 2016 and 15th April 2016. Out of 15,312 customers who responded, over 94% rated OVO 6+ when asked 'how likely would you be to recommend us to a friend and family, on a scale of 1 to 10.

Britain's top rated energy provider: Britain's top rated energy provider in the Which? 2015 satisfaction survey. Survey conducted in October 2015. Awarded in January 2016.

uSwitch's Energy Supplier of the Year: OVO energy was voted and awarded  'Energy Supplier of the year' and best for: Overall Customer Satisfaction, Most Likely to be Recommended, Value for Money, Best Deal for You, Customer Service, Billing Services, Energy Efficiency, Meter Services, Online Services, Green Services and Transfer Process. OVO Energy scored a 96% customer satisfaction score.

Which?: Achieved the highest score of 78% in the Which? Satisfaction Survey conducted in September and October 2016.

* EV - Everywhere, full terms and conditions:

* OVO SolarStore (Beta), full terms and conditions:

Pay Monthly unit rates

PAYG unit rates

Read more Read less

Like most websites OVO Energy uses cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we'll assume that you are happy to receive all cookies on this site. Accept and Close