The Ultimate Beginner’s Guide to Energy Saving Light Bulbs

Energy Saving Light Bulbs

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 fittings

‘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.  ‘GU’ is for, gee you really need to get yourself a life a if you know what ‘GU’ means.

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.

bulb shape

There is literally an alphabet describing different bulb shapes, but since I promised not to bore you I’m just not going to go there. All you need to do for shape is use your common sense.

For a ceiling pendent you might want an ‘omnidirectional’ bulb like the arbitary, 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’ is 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.

Now I’m very sorry to do this, but 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.

Lumens US

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 High Voltage Lumen (UK):

In the rest of the world grids have higher voltage, meaning that lumen equivalent for standard incandescents is different.

Lumens needed

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:

Just spot me a second here.  Both the two 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 is dead easy and 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.

kelvin scale lightbulbs


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 (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 style 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 quite 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 $10, assuming the bulb is used for 2 hours each day.

LED payback times

Because of the huge difference in the prices of electricity the $10 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.

Of course a 60W LED for $10 is still quite cheap.  If it costs you $20 to get such a bulb you’d need to double these numbers.  On the other hand if you are using the bulb 4 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 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 (>2 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 (< 1 hour a day) you may want to wait for falling prices.  Especially in the 100W replacement range which are still extortionate.

I have one incandescent left in my loft that I’d be lucky to use for 10 hours a year.  I’ll probably only switch it if it blows.

5 Steps to Buying a 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 not to discuss 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 trialing 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.

Here in the UK I’m on the lookout for decent 10W LEDs around the £10 mark. This Verbatim LED 10,5 W  verbatim is a great deal for £9.99.  Or something like this 10 Watt LED (or in a screw fit).  I’ve just bought this Philips Master because I’ve always liked the look of it and saw a big price drop .  For bathroom or kitchen spots I prefer LEDHUT.

Looking over the pond to the US I’m almost jealous. You guys get similar 10W LEDs for $10.  This great 11W LED Dimmablefrom Phillips (complete with Energy Star rating) for $15.  Interesting slim style bulbs. Your LED spots  are cheaper too.  And you can buy remote controlled color changing LEDs  for just $13, which is not boring!!

If you made it the end, thanks for reading.  I wish you much success with your LED hunt and 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, as that is the main test of success.  This post is one of the efficiency projects connected to our How to Save Money on Electricity video program.  If you enjoyed it you should go check it out.

30 Day Shrink Guide
  • Kiwiiano

    One warning about CFLs: part of their life expectancy is determined by the number of times they are turned on. Each time a tiny wisp of mercury atoms are boiled off the amalgam until it is depleted and the lamp dims to a faint neon pink glow. CFLs are best installed in situations where they are left running for long periods. Constant on-offs, like toilets, or bathrooms shorten their lives. Outdoor PIRs can kill one in a month or less if they are being affected by wind-blown foliage.
    LEDs have no such problems, are happy being pulsed hundreds of times a minute. In fact, I think they will supersede CFLs in a year or two.

    • Lindsay Wilson

      Hey, thanks for the great comment. That really adds some value. It does feel like CFLs were the ‘CDs’ en route to digital. I wonder if a lot of people use CFLs in motion sensor lights? The slow warm up speed seems to make them bad for that too. Just two years hey? I’m hoping most LEDs will come down below $10, that should make them truly mass market pretty quick

      • Kiwiiano

        I did, and lost the CFL in 3 weeks. I don’t recall any problem with slow warm up at the time and have several CFLs round the house that come on at about 80% full brightness. Others start at about 30%, if that. I suspect that following the hysteria they’ve reduced the mercury content to the point CFLs are struggling to perform at all.

        See and search for “LED bulbs” for LEDs below $10 (incl free postage). We were selling complete LED MR16 pivoting downlights for NZ$27 at our local Bunnings. Also noteworthy because the LEDs were permanently soldered in situ.

        • Lindsay Wilson

          I’m just starting to see the in situ stuff coming through in the UK. I know people who had epic electric bills due to colossal halogen installs, and they just love the things since it slashed their bills

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  • Bob Ashworth

    Excellent guide to LED lighting. Thanks for posting it.

    The house my son bought had 9 halogen 50w bulbs in the kitchen, which had to be switched on in banks of 5 and 4, but often were all on. He has replaced them with 5 watt LEDs and it has not only slashed his consumption, but it has given a much pleasanter light.

    As the kitchen is the most used room in the house the lights are on alot of the time, especially in the UK winter. He has calculated they will recover their cost in less than two years, which fits in with your estimate above.

    • Lindsay Wilson

      Thanks Bob, I swapped 8 halogens for lower lumen leds and was astonished by how much more I enjoyed the light. Better yet, in my local cafe the halogens kept blowing due to poor insulation. I helped them swap about 50 of the things. Because it was a bulk buy and they are on 12 hours a day payback was comically fast, just a few months. The prices are really coming down on spots so in high use areas like kitchens they are a great shout, especially if you want a cooler light

  • Roberto Rodriguez Labastida

    If you are replacing spotlights it’s also useful to play with different light angles. Wide beams work well in larger areas or when you need ambient lighting. Narrow beams are great to climate specific areas of a room. As lumens are distributed in your beam, you can use lower lumen bulbs for narrow beams without losing intensity.

  • Alberta E. Crane

    There is a very good calculator that works out the cost of LED vs traditional bulbs but also builds in replacements costs for both. I think this must be assuming current prices but you can add inflation for energy costs. It is worth having a look at. Goto and then click the savings calculator.

    • Lindsay Wilson

      Its a shame some of the presets are so bizarre, but its a good calculator nonetheless

  • Kendra Turnbull

    Through our environmental charity we have a LED light bulb library so that people can try different colours, shapes, lumens and wattages in their own homes. People are often amazed (and slightly overwhelmed) by the choice that LEDs offer in comparison to CFLs. It really does encourage more people to swap and reduce their electricity consumption levels.

  • Greg Alexander

    Good starter article!

    I’m interested now in learning about directional bulbs – I’ve seen a globe with bayonet fitting that puts all the light out one side. So if you have a sideways bayonet fitting in your ceiling light, the bulb only puts out light downwards, not upwards. But I kinda like having my ceiling lit a little…

    The other thing I’ve just heard about is high or low CIR – apparently some LEDs don’t give a full colour gamut, so while measurements show the same ‘peak’ brightness a full CIR has more perceived light? (Like how sound on commercials is louder by keeping the peaks low but having a ‘fuller’ background sound.) Still learning…

  • Max

    Good information here, thanks. Do you know why manufacturers often indicate lumen as well as candela? How are these units related and would you say that one is a more useful indicator for brightness?
    Looking for energy saving light bulbs I found this website:
    They have a lot of products from Philips and Osram for a decent price so guess I am going to order my lamps there.

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  • k_nonymous

    This was very informative. Thank you. I kept getting CFLs with the wrong color temperature. 2700K it is from now on.

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  • sujal

    what is the difference between cfl led simple bulb and led??

  • June

    Open and find LED lights from Taiwan suppliers! Low price and high quality!

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  • Mariappan Srinivasan

    LED saves energy and enviro friendly. It emits very very negligible heat energy to the environment over CFL and Incandescent Bulbs