Energy Efficient Lighting Pt 1 – CFLs

by Jamie on March 30, 2010 · 3 comments

The widespread roll out of compact fluorescent lamps (CFLs) has caused quite a stir to say the least – these innocuous little things have upset quite a lot of people, with some feeling the need to take drastic action.

Certain sections of the press definitely haven’t helped, spreading some pretty extraordinary stories about CFLs over the last few years; stories which have been designed to spread confusion and fear of what is a very good and safe energy efficiency technology.

People have been working under fluorescent lighting for decades and a CFL is not very different to an office fluorescent tube – it’s just been folded up on itself into a much smaller space.

That’s not to say that they’re without fault. They contain a very small but significant amount of mercury and therefore need to be handled appropriately (more on that in a future post), in some cases they can take a moment to warm up which is not what we’re used to after a century of incandescent lighting and the light that some give out is not the best.

Another problem is that a lot of unsolicited bulbs of varying quality have been distributed under the Carbon Emissions Reduction Target, with people receiving bulbs through the post with the wrong fitting, bulbs that give out a harsh light and bulbs that looked, well… pretty damned ugly.

But it definitely doesn’t have to be like this so this post is dedicated to the things to look out for when hunting for the perfect CFL.

CFLs use about a quarter of the electricity of a conventional incandescent. This is a big saving and one that means that you shouldn’t wait until an incandescent bulb blows before replacing it.

The embodied energy of a CFL (the energy used to produce it) is greater than the embodied energy of an incandescent bulb, but the efficiency savings you get from using CFLs greatly outweighs this additional energy so swap all your remaining incandescent bulbs today.

Defra has published a comprehensive life cycle assessment of ultra efficient lamps which is worth reading if you want to know more about the environmental impacts of different lighting technologies.

You can pick up very cheap (often subsidised) CFLs all over the place nowadays but I find it’s worth spending a few pounds on really good quality bulbs. On average a CFL will save a few pounds each per year and if it’s replacing a high use bulb it’ll save you a good deal more than that and over the lifetime of the bulb they will save you anywhere between £50 and £100 per lamp.

In different situations you might be looking for different qualities in your CFL. For example on an upstairs landing you might want one that warms up quickly, in the living room you might want a warmer light while in the kitchen you might want a bluer and brighter light.  As these types of bulbs last for a good 10,000 hours, it’s worth finding the right one for your needs.

The thing that many people seem to object to most is the colour of light that CFLs give out, known as the Colour Temperature.

You can buy fluorescent lamps in a range of colour temperatures from 4000K (or 4000 Kelvin, sometimes known as “cool white”) which gives a stark, blue light, to 2700K (sometimes known as “warm white”) which gives a much warmer colour very similar to incandescent bulbs. Natural daylight is very blue and has a colour temperature of about 6500K.

For most people this lower colour temperature (which confusingly gives a “warmer” colour) is what they should be seeking out.

Another measure of the quality of light which a bulb gives out is the Colour Rendering Index. This measures how faithfully the colour of  a surface appears under different light sources compared with an ideal light source.

The scale measures up to 100 and the higher the CRI the better. You can buy CFLs with a CRI of over 80.

Efficacy is a measure of how efficiently it converts electricity into light and is measured in Lumens per Watt (Lm/W). You will sometimes see CFLs with the same power consumption but different Lumen output (i.e. one is brighter) and this is an example where one lamp has a higher efficacy than the other.

The use of Watts to describe a bulb’s brightness is being phased out at the moment and you’re going to be reading a lot more about Lumens in the future (both will be displayed on packaging). It makes a lot more sense to use Lumens as this is a measure of brightness whereas Watts are a measure of power consumption.

The following table gives the brightness that incandescent lamps of different power give so you can work out what brightness a replacement CFL should be.

The “clear” column gives the brightness of incandescent bulbs made with clear glass and the “soft” column is the brightness for the frosted sort of bulb:

Power (W) “Soft” Brightness (Lm) Clear Brightness (Lm)
40 335 365
60 575 620
80 830 895
100 1075 1175

(Source: EST Lighting Specification)

In common with all lights, including incandescent bulbs, CFLs lose some brightness over their lifetime, but if you buy a good quality bulb they will give a good light output for a very long time.

A bulb’s start up time is also important for many people. CFLs switch on very quickly (less than a second) but then take a while to run up to full brightness. They can take up to a minute or so to reach their maximum brightness, but what is most important is how quickly they get up to a reasonable brightness.

If start up time is important to you then look for “fast start” bulbs that warm up quicker than regular bulbs. In some cases I find it’s nice to have a slow warm up time, especially in bedside lights so that you’re not blinded in the middle of the night.

So that introduces the technical aspects to look for. Size and shape should also be considered as some CFLs won’t fit as neatly in a lampshade as others but there is now such a huge range out there that you can find excellent bulbs for nearly every situation and the number of good quality bulbs is growing all the time.

For the record, my favourite CFLs are made by Megaman but there are a load of good ones out there. At some point I might do a post collecting together the best bulbs from each manufacturer. Feel free to post your favourites in the comments below.

In future posts we’ll look at other aspects of lighting such as halogens, what to do if you have dimmer switches and other technologies such as LEDs.

Power (W) “Soft” Equivalent Clear Equivalent
40 335 365
60 575 620
80 830 895
100 1075 1175


1 tom hitchman March 31, 2010 at 9:18 am

Thanks Jamie a great and illuminating article!

On one of our ‘Carbon Conversations’ groups one member was clinging on to her old bulbs as she didn’t want to waste the embodied energy. She soon fixed that after a discussion changed all her bulbs and was off. A colleagues (the group was run in an office) then brought in all the CFLs that had the wrong fittings for their home and left in a box in the kitchen area which spawned many people to do the same, emptying out the unused ones from their kitchen drawers! It started a very small and useful revolution in their office and are now planning to have a freecycle box every other friday for unused good for their staff. Its funny how a little conversation can yield much more than you would expect.

Wondering if the pangea project might donate a cardboard box for this too?

2 Jamie March 31, 2010 at 5:35 pm

Ah yes someone (possibly you) was telling me about that. Really good idea! PP has limited space but I can see if they might be amenable. Otherwise I could look after them and bring them along to TT events from time to time. Will have a think….

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