greentomatoenergy’s guide to buying LEDs

Although statistics vary, somewhere between 16% and 19% of global power consumed is used for lighting.   It therefore makes sense to look at how efficiencies can be made.

Incandescent lightbulbs need to be replaced – in an incandescent lightbulb (for the purposes of this blog halogens work in a similar way), electricity runs through a very thin tungsten filament, which heats up to about 2,500°C and then glows, thereby emitting light.  However, whilst the light emitted is good quality light, approximately, 90% of the energy consumed by such lightbulbs is given out as heat, only 10% is converted into light.  This means that much energy is wasted, which is why they can’t be used.

..by another type of lighting There are two types of more energy efficient lighting.  Compact Fluorescent Lights (CFLs) or 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 and the lamp’s coating converts the ultraviolet light into visible light.  Less of the energy is used in producing heat and less is wasted. However, the trouble with CFLS is that as they contain mercury, they are 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 a collection of LEDs has been used to form images on TV screens.  A very simple explanation of how they work is that they are illuminated by the movement of electrons in a semiconductor material.  A much lower proportion of the electricity used in LEDs is used in generating wasted heat and as they don’t have a filament that is prone to burning out, they last much longer. They contain lots of different components and are therefore more expensive than incandescent bulbs, halogens and also CFLs.  Your existing bulbs can be replaced with LEDs directly or you can replace the whole fitting.

..which requires a bit more careful choosing

  • Brightness – 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, so check the packaging.  To give you a very rough idea of the scale on which lumens work:


–         a 40W incandescent bulb around 390 – 460 lumens

–         a 60W incandescent bulb is equivalent to around 750 – 850 lumens

–         a 100W incandescent bulb is equivalent to around 1,700 – 1,800 lumens.


  • Colour temperature – LEDs allow you to choose from a greater range of colour temperatures. This 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 controls sometimes causes the light to spread at a wider angle.  You just need to think about what you want.

  • Guarantee – 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.


  • Dimmers  – by far the most common problem we find once people have purchased blub 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.  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, it’s quite key that the LED dissipates heat properly, otherwise the components could fail.  If you’re changing the fitting and making the area airtight, it’s worth discussing it with us first.


  • What else? There’s a lot to think about.  Most brands enable a trial period.  You can then test out colours, beam angles etc. and ensure that you’re making the right decision.  There is also a very great variance in quality as between brands, particularly as there are so many components.  Make sure you look at reviews, time in the market etc..