Are low energy light bulbs really as effective as claimed?

Compact fluorescent lamps (CFL) are set to become the most common type of lighting used in homes across Europe.  European legislation has already banned the manufacture and import of all 100W incandescent bulbs as well as all frosted bulbs.  In 2011, 60W bulbs will go, while 40W and 25W incandescent light bulbs will be gone by 2012.  But are these bulbs really as effective as claimed?


If you think your new CFL bulbs aren’t as bright as incandescent bulbs you’re probably right.  The reason is that CFLs don’t necessarily produce the levels of brightness promoted on their packaging.  Since CFLs have a phosphorous coating they are compared to frosted incandescent bulbs when calculating an equivalent brightness.  But most people use clear incandescent bulbs which are brighter so the comparison is not strictly accurate and means that most low energy bulbs aren’t labelled correctly.

The European Commission’s advice is to divide the wattage of an incandescent bulb by 4 to get the equivalent brightness e.g. to get the equivalent of a 60W bulb you would require not an 11W bulb but a 15W bulb.  But the Lighting Research Centre in the United States goes further by suggesting a factor of 3 should be used.  This is because compact fluorescent bulbs aren’t as bright if they fitted into a room that is too hot or too cold, take time to reach full brightness and significantly dim over time (up to 20%).  So if you want the brightness of an incandescent 60W bulb you will need an equivalent 20W CFL.

New European regulations expected this year will mean manufacturers will have to display lumens – a measure of light output – more prominently than wattage on bulb packaging.


The Energy Saving Trust, European Commission and manufacturers claim CFLs use up to 80% less electricity than incandescent bulbs.  But how is this number calculated and does it add up?

It’s worked out by comparing the best compact fluorescent lamp’s wattage with the wattage of an equivalent incandescent.  But that results in a 5:1 energy ratio between the two – a claim exaggerated when manufacturers use it although the words ‘up to’ are usually used.  However the EC says the saving can be as low as 60%.

John Henderson, an energy expert from the Building Research Establishment, says “when you see an 80% savings figure on the side of a low-energy light bulb, it doesn’t actually mean that you’re going to save 80% lighting energy, 80% carbon emissions, and 80% costs.”  Traditional bulbs expend about 95% of their energy producing heat whereas CFLs convert most electricity into light.

The European Commission considers this to be heat loss.  But Mr Henderson disagrees. “Let’s say your house uses 1,000kWh a year to produce the light you use.  If you were to replace all the old-fashioned light bulbs with the modern low energy lamps, you might expect an 80% reduction – 800kWh.  However you’d find about 60% of that 800kWh would get automatically chucked back in by your thermostat-controlled heating system.  A typical heating system is only about 75% efficient.  So the actual figure you end up with is more like 240kWh a year, rather than the 800kWh you expected.”  That number is only a rough guide, as most homes have gas central heating which is cheaper and less carbon intensive than an electric heating system.

The Institute of Lighting Engineers is considering changing its estimate of the energy savings represented by CFLs from 80% to 70%.  This is because the power factor of CFLs is low, which means a utility company needs to use more energy to get these lights to work, which can also cause disruptions in the power network.


You will get what you pay for when it comes to bulb lifespan.  While a branded bulb from a well-known manufacturer may last the promised 10 years, one from a supermarket may not.  But even branded bulbs don’t always last as long as expected – this is because the lifespan given is an average.  When a batch of bulbs is tested, they are turned on for three hours, then off for 20 minutes over and over again until half the batch fails.  This time is then denoted the average life.

It is often 10,000 hours.  As no-one adds up the hours a light is on over its lifespan, this is translated as 10 years, on the assumption that the bulb will be on for an average of three hours a day.  But as half the bulbs will fail before 10,000 hours, a consumer may be unlucky enough to pick a dud that will fail after just 2,000 hours.  However, the main manufacturers do their best to make bulbs last around the average lifespan.

How you use a bulb can also affect its lifespan.  Continuously turning it off and on every 15 minutes may cut its lifespan to just 4 years so its probably worth keeping lights on when simply leaving the room for a few minutes.


The most important environmental impact of lighting is the energy used during its use.  So from an energy perspective at least CFLs are preferrableto incandescents.  Energy used to manufacture the bulbs is important but there seems to be some debate over this at the present to comment.

However another issue to consider is the small amount of mercury used.  Manufacturers are working to reduce the amount used but the effect is minimised if the bulbs are recycled.  Incidentally, most commentators agree that more mercury is put into the atmosphere by old-fashioned bulbs than CFLs, due to the coal burned in power stations to produce the extra electricity they consume.


On balance, although the claims made for CFLs appear to be exaggerated they still offer significant energy, cost and environmental benefits.  However we should expect labelling to improve as the bulbs become more common, technology improves and policy develops.

There are other energy-saving options such as halogen tungsten lights which are about 30% more efficient than incandescent bulbs.  Technology is developing fast, so it could be only a few years before people are lighting their homes with LED lights, which experts say have the potential to be more efficient than CFLs.

LINKS                                                                                                                                                                                             Ethical Consumers Buyer’s Guide

More or Less podcast (the inspiration for this post)

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  1. ‘If you think your new CFL bulbs aren’t as bright as your old incandescent bulbs you are probably aren’t imagining it.’

    What does that mean? Am I, or am I not imagining it?


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