

The Ultimate Beginner’s Guide to Energy Saving Light Bulbs



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.


3) How bright does it need to be?


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.


The American Lumen:


the american lumen


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?


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:


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


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.

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