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How to choose low energy lightbulbs

Posted by greentomatoenergy . on 20 September 2013 at 9:20 am

Somewhere between 16 and 19 per cent of global power consumed is used for lighting so it makes sense to look at how efficiencies can be made.

Traditional lightbulbs, also known as incandescent bulbs (for the purposes of this blog this includes halogens), work by passing electricity through a very thin tungsten filament. The filament is heated to about 2,500°C causing it to glow and emit light. Whilst the light emitted is of good quality, approximately 90 per cent of the energy consumed to create it is given out as heat, with only 10 per cent converted into light. This means that much energy is wasted. 

So what is the alternative? There are two energy efficient alternatives to incandescent lightbulbs: compact fluorescent lights (CFLs) and light emitting diodes (LEDs).

A CFL is like a strip light you would find in an office. It contains a combination of argon and mercury vapour which produces ultraviolet light when electrified. The lamp’s coating then converts the ultraviolet light into visible light. This method produces less heat so less energy is wasted. However, CFLs do contain mercury making them difficult to dispose of.

LEDs have been used since in 1960s in a number of applications, such as the figures on digital clocks, backlights on watches, in remote controls and TV screens. Put simply, the light in an LED is created by the movement of electrons in a semiconductor material. With an LED, a much lower proportion of electricity is wasted generating heat. LEDs contain lots of different components and are therefore more expensive than the alternatives, but since they don’t have a filament that is prone to burning out, they last much longer. Your existing bulbs can be replaced with LEDs directly or you can replace the whole fitting.

What to consider when choosing LEDs


We used to be able to tell how bright a bulb is by looking at the number of watts. This doesn’t work when choosing LEDs because they don’t need lots of electricity to make them brighter. You therefore need to look at the number of lumens.  A lumen is the standard unit of light as it is perceived by the human eye and the lighting industry now includes the number of lumens on their packaging to enable you to choose. To give you a very rough idea of the scale on which lumens work:

  • a 40W incandescent bulb is equivalent to 390 - 460 lumens
  • a 60W incandescent bulb is equivalent to 750 – 850 lumens
  • a 100W incandescent bulb is equivalent to 1,700 – 1,800 lumens

Colour temperature

LEDs allow you to choose from a greater range of colour 'temperatures' from bright white, or 'cold' light to 'warmer', yellower hues. Colour temperature is measured in degrees kelvin.  2,700k is about the same colour as a halogen lightbulb, which is a little bit yellow.  A colour temperature of 3,000 – 3,200k  provides a more neutral colour without being overly bright white.

Beam angle

If you’re replacing halogen spotlights, you need to confirm what beam angle you’re looking for. Halogen spotlights have a beam angle of around 36-38°, but a lot of halogen spotlights contain a reflector which sometimes causes the light to spread at a wider angle. If you're happy with the angle of your existing halogen spots, then choose an angle that's similar or slightly wider, from your LED.


LEDs last much longer than incandescents (50,000 hours versus 3,000 hours) and are more expensive. They are therefore guaranteed by the manufacturer. A standard manufacturers’ guarantee is three years.


A common problem people find once they have purchased bulb replacements, is that the LED is not compatible with their dimmer. Sometimes, even dimmable LEDs don’t work with an existing dimmer. You need to check compatibility with your supplier. Many good brands and suppliers offer either a free sample bulb, or a no-strings-attached, week-long trial. If you take a trial of the lights, you’ll soon find out whether it works.

Heat dissipation

Whilst LEDs generate a lot less wasted heat than incandescents, the LED has to dissipate the heat it does produce properly, otherwise the components could fail. If you’re changing the fitting and making the area airtight make sure you discuss it with a good supplier or an energy surveyor first. 

What else?

There’s a lot to think about. It's always a good idea to accept a sample bulb if offered, so you can test out colours, beam angles and brightness to ensure you’re making the right decision. There is also a very great variance in quality between brands, particularly as there are so many components. Make sure you look at reviews, the length of time a brand has been in the market and guarantees. 

Akta Raja is a founding member and director of greentomatoenergy which installs solar panels, conducts energy surveys and designs low energy buildings. 

More information about energy saving lighting

The YouGen guide to low energy lighting

From the blog

Consumer group finds the brightest energy saving light bulbs

How to dispose of energy saving bulbs

Comparing costs of lightbulbs: upfront costs vs running costs

About the author: greentomatoenergy specialises in cost-effective renewable technologies and low carbon building.

If you have a question about anything in the above blog, please ask it in the comments section below.

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3 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 10 November 2014 at 9:40 am

Hi Paul

It depends what you want to achieve. Is it low bills? Low carbon emissions? Both? Because I don't like waste, and chucking out things that work, I've done the big ones - ie halogens to LEDs, but am only replacing cfls when they blow.

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paul53Comment left on: 8 November 2014 at 6:49 pm

having  upgraded  my lounge lights from  6  18 w leds to  6  4w leds , the  rest of the  house being on  cfls is  it  worth  updating the  rest  to  leds if  they will only  be in use  a couple  of  hours a  night in  winter.and  untill the  supplier update s my  meter, my  bill is  still negetive i realise it will  only be  months before  a new meter is  fitted  

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osbrookComment left on: 1 October 2013 at 3:51 pm

Excellent article covering all the areas I have found over the last 5/6 years of using LED bulbs.

I now use 240V GU10 LEDs
12V CFL fitted in standard B22 fittings
1000's of LED strips running at 12V

The 12V all run from a battery bank powered by separate Solar PV panels form the Roof Grid tie ones.   The intention is after a few months of winter testing to migrate the rest of the house to 12V lighting (both CFL and LED).

Our house hold prefer Cool White  or Day light white over the traditional warm white.


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