/ Home & Energy

Are your LED light bulbs burning out too soon?

LED light bulb

LED light bulbs have a tendency to make grand claims about their lifespan – it’s common to see manufacturers promise bulbs will last 25,000 or even 50,000 hours. But we’ve found many failing well before this.

One of the attractions of LED light bulbs is that they’re supposed to last a long time. And so if you’re shelling out for these bulbs – typically more expensive than other types of light bulb – you’ll want to be sure that they’ll live up to those claims.

But our tests show that not only do many LED light bulbs stop working before the end of their promised lifespan, some don’t even reach the soon-to-be-implemented EU minimum lifespan of 6,000 hours. We discovered bulbs from both Ikea and TCP that failed to reach the 6,000 hour mark for the majority of samples we tested.

Ikea bulb among failures

In the tests – which were carried out by Which? and our European partner organisations – we took five samples each of 46 different bulbs. The bulbs were switched on for two hours and 45 minutes, then switched off for 15 minutes, in a continuous cycle until they burned out.

Five different bulbs stopped working before the 6,000 hour mark for the majority of samples we tested, though the TCP and Ikea bulbs were the only ones which were sold in the UK. Both have since been discontinued.

New EU regulations which will come in from 1 March 2014 say that 90% of any batch of LED light bulbs should last at least 6,000 hours.

Another five bulbs stopped working before the 10,000 hour mark for the majority of samples we tested, despite claiming lifespans of at least 25,000 hours. None of these bulbs were sold in the UK.

In total, 66 of the 230 samples we tested failed before the 10,000 hour mark, though they all claimed they would last at least 15,000 hours.

Has your bulb burned out early?

Ikea said the bulb had passed its own tests and those in a third-party lab. It’s looking into why the bulb failed our test and has removed it from sale in countries where it was still available.

TCP said it was already aware of the problem with this bulb and withdrew it from sale when they discovered the problem. TCP added that it no longer deals with the supplier of that particular bulb and now make their LED bulbs in-house.

We’re in the process of testing the life span of many more LED bulbs, and we’ll update you if we find others that burn out prematurely. But we also want to hear from you – have you bought bulbs that haven’t lasted as long as they should?


One problem with LEDs is that suppliers make them to go into products for which they are unsuitable – like high power bulb replacements or spotlights that then run too hot. Use LEDs for their strengths – with proper cooling, not crammed into a small space; use decent electronics. This is what is done with them in commercial applications, street lighting etc. – those clients would not tolerate failures of the type discussed here. The same applies to CFLs – commercially they have separate electronic ballasts that control the lamp better, are more efficient and aren’t discarded when the lamp fails. Such lamps, however, generally require luminaires (light fittings) designed for them. The target for domestic lighting seems to be plug-in replacements for the older technology – the premise being, presumably, that we won’t spend the money on a new luminaire. Maybe they are right? If you want decent LED luminaires, visit a UK LED luminaire supplier on the web and see what they can offer.

One of the reasons that commercial lighting is generally of better quality is that it costs a fortune. You pay for quality. Having said that, the most spectacular example of failure of LED lighting was some recently installed pavement lighting in a city, which I described in one of the Conversations.

Phil b says:
26 January 2014

Not had a very good track record so far. Mnufacurer CED model GU6WW type GU10 5.4W 240V. One of theses failed after only a few months (problem with driver circuitry, light would flash on and off) a second failed after about 2 years in a room that is not use that much.

Phillips Master LEDspot LV lasted about 3 years (probably around 2,500hrs, so about 10% of predicted life). Theses apparently contain a fan to cool the unit…… a mechanical fan that lasts 25,000hrs always seems optimistic and i think this is what caused the failure of the bulb. So £28 for this bulb was a very bad investment.

Whilst I see a great future for domestic LED lights and have so far installed 10, I’m not happy with the failure rate I’ve experienced. Four GU10 bulbs (ranging from 4W to 6W) from one online supplier failed within a year or two and I’ve now stopped buying from them. A fifth from another supplier failed after 2 weeks but was replaced free of charge. However, I’m reluctant to install more at the moment until I’m confident their lifespan is sufficient to justify the cost.

Nick C says:
26 January 2014

Don’t be too discouraged – don’t forget that it generally only takes 1,000 hrs to recover the cost of an LED lamp so their cost (depending on how much you paid) will probably have been recovered, and if you average across all the lamps you bought you will be many pounds in credit.

Also, don’t forget how often many old-fashioned, inefficient lamps blow – since replacing all of the 50w halogen downlight bulbs throughout my home with LEDs I have been delighted at the low failure rate in comparison.

I know that it seems to be human nature nowadays to focus on the negative when anyone recommends anything new, but I worry terribly that we end up throwing the baby out with the bathwater. There’s a balance to be achieved in any assessment and in my personal view LEDs already, at such a relatively early stage in their development, greatly outweigh the old-fashioned alternatives.

This 1000 hours is not appropriate when comparing an application that you could meet with either an LED bulb or a spiral CFL. As in an earlier post, it could take around 15 years (30 000 hours) to recoup the extra cost of the LED. It all depends upon the application.

Nick C says:
26 January 2014

But most people are comparing using old-fashioned bulbs with new ones. Agreed that CFL lamps would probably work out cheaper than LED, but most people have rejected those because they don’t like the way they take time to come up to full intensity or don’t give the quality of light they like. If these are not issues then CFL is still a good and even more reasonably priced alternative than LED.

However if they want the same characteristics as they get with old-technology lamps then LED is the only answer, and the price comparison between them stands.

I just don’t understand why people are so determined to prove that newer technologies are no good. Nothing is perfect; it’s just a case of working out which is the best of all available alternatives, and the saving in money terms (and other public good terms) of higher efficiency lighting is substantial.

Nick “But most people are comparing using old-fashioned bulbs with new ones.” I think most people are looking for the best solution – which lamp, overall, best meets their needs. This has nothing to do with not embracing new technologies (white leds are hardly new). CFLs from decent manufacturers have good colour, instant start and good run up to full light output. As have good quality LEDs. Comparing GLS, LED and CFL is perfectly valid. “Most people” have not rejected CFLs, no more than “most people” would reject LEDs because of a tranche of criticism. Buy quality lamps, decide what you need, compare the costs and “most people” will arrive at their own conclusion.

Nick C says:
26 January 2014

If only that were the case! In my experience most people seem to find any and every reason to stick with old-fashioned lamps. They do arrive at their own conclusion, but it is not in general a balanced one formed on the basis of a common-sense evaluation of the pros and cons of the different products that are available.

It always amazes me how innately conservative people are, and they grab hold of any reason they can find for sticking to old-fashioned products. And it’s not necessarily the truth they base their views on – I agree that modern CFLs are pretty good nowadays, but they are not perfect and that is all the excuse people need. Lack of full output on switching on, less good colour rendering, and the near-hysteria put about by the media (DM, I’m looking at YOU!) regarding mercury in the lamps have been more than enough meat even though they are not that big a deal in the balance.

Now we are seeing the same reaction beginning all over again about LEDs, and it would not surprise me to start hearing people countering them very soon with the story that they “all fail way before you get your money back”. And then the damage will have been done, just like with CFLs.

The only way to counter this is to make sure that a more balanced view of their pros and cons is communicated at every opportunity, even though that is sadly not the way that certain sections of our media work. They just love to destroy things if they can without any regard to the consequences.

With a new house I have had the opportunity to install new lamps throughout and most of them are CFL’s. Compared with the early CFL’s in our previous property the latest ones give a much better colour rendition, start quickly almost instantaneously in most cases] and look more attractive where they are visible. I have even found a very good large 35W spiral CFL at B&Q that gives a light output approximately equivalent to an incandescent 150W bulb [2285 lumens/2700 colour temperature/10,000 hrs advertised life/£9.98 currently]. In a large off-white glass shade it gives a very even, virtually shadow-free, light spread and reflection off the ceiling. I am so impressed with it I am going to get some more for other places where we want high light levels from a central fitting. Personally, I think the CFL gives a good combination of reasonable purchase price and economy in use. Over the years, I have had to discard a lot of CFL’s because they failed prematurely or they became too slow or dull [we know some people like that too but it’s not so easy to replace them] but I think at last the product is about right and the price & running cost are acceptable. I expect we have some way to go with the LED price/performance equation before we get to the same satisfaction level.

One of the reasons why I have been reluctant to go down the LED route is that when we actually looked at the number of hours each light is on each day, it is surprisingly small. Even the kitchen has lights on for less than an hour a day. With good natural light available in most parts of the house and the use of task lighting and table lamps the energy bill for lighting is the least of our worries. Replacing nearly new CFL’s with LED lamps would not make financial sense and might even be a bad move if reliability and endurance are as poor as reported.

John – If you were using decent quality CFLs, I suspect that overheating may have been the main reason why you have had failed lamps, especially the higher power varieties. Lampshades that allow a free flow of air will help provide cooling.

I have not switched from incandescent bulbs in a centre light fixture because there is no ventilation in the shades. I did try CFLs but removed them promptly when I realised that the lamp bases were becoming far too hot. LED lamps are no use for the same reason and also they would not produce sufficient light.

I am not tempted to buy any LED lamps because it seems likely that the technology will improve and the price will fall. For most purposes I’m very happy with CFLs.

I was going back over twenty years I think, and when I said “prematurely” I suspect it was because they failed after four years when I was expecting six years’ life! The main reason for any replacements was to increase the light level or improve the appearance [some of the early CFL’s were downright ugly], or because the whole fitting was replaced and I took the opportunity to fit the latest lamps. Certainly it is essential to ensure that the lampshade does not enclose the lamp too closely. I just discovered that my desk lamp still has an incandescent bulb under its green shade; that must have been there a very long time as I cannot recall ever changing it.

allen says:
30 July 2015

Really? Which bulb company do you work for?I Buy 3 Cree 3 ways in 11/14 and two have died. This is a sham and just poor quality. They haven’t responded to my return after a couple weeks still waiting can’t see any economics here. $21 a bulb and 4 to return with no replacement yet. I’m 74 and seen this crap before in other products.

The good news is my failed 5 6 week old LED GX50 lights have been replaced, and the other 9 too probably. A faulty batch apparently. I will probably put spacers under the mounts to improve cooling and hopefully get a longer life. They still use some power and stay warm even when they have failed; not very economic.
One point not really being addressed is how many light fittings we need now compared with the days of incandescent lamps to get passable lighting levels.
When we were first married we had 1 60 watt fluorescent tube + 1 pendant in the kitchen. 1 150 watt pendant and 3 60 watt par reflector lamps in the living room. (The last 3 rather new at the time; I did amateur dramatics stage lighting then too) A master dimmer controlled the lot in that room. Yes a lot of heat but only wasted in summer remember, when the evenings are short anyway.
Now in the present house we have numerous ceiling spots plus pendants in the slightly larger living room, some dimmable, and 1 pendant plus 2×3 surface ceiling spot lights plus 14 leds in the kitchen.
Yes it looks good but it is debateable if lighting levels are as good in general, and what about all that extra wiring and switches, and the more lights you have the more often you will be on the steps replacing one. I will no doubt replace many of these with leds eventually but they have a long way to go as regards output and reliability. My old crown silvered lamps in the corridor and bedroom, used every day lasted 15 -20 years between replacing, even better than old fluorescents.

I am a fan of table lamps in the living room and bedrooms – apart from giving a good, but varied, general light (better than ceiling pendants) you can position them near to where you read – usually the most demanding task – and fit appropriate power bulbs. And, of course, you only need switch on those that you need to use at the time. Good with the TV as well.

Will says:
28 April 2015

It could take 15 years, but it could also take less than a year. Upon switching our 8 kitchen lights over, we’re now saving 7-8 quid per bulb per year averaging 3hrs/day use. Each bulb costed 6 quid. You do the maths.

Honestly, LED brightness is fine. Just buy the right brand. A 12w Integral GLS puts out staggering light, more than a 75w incandescent indeed!

Will, equally, if a CFL was suitable, you could save £5-6 a year by using these – more proven reliability. When people have problems with LEDs it is largely that they do not last, so the economics fail them.

Precisely. In ten or fifteen years, CFLs may be obsolete, but for now they seem to have fewer problems.

No-one has even mentioned that LEDs with a light output equivalent to the humble 100W lamp are not readily available, whereas high brightness CFLs are readily available.

CliveH says:
26 January 2014

In October 2011 purchased two 12v LED spotlights at £24.99 each from LightPlanet who also trade as ocgtechnology.com. The bulbs were Altled Aurora MR16 series made by Aeon Lighting Technology Inc of Taiwan.They were 7w LED GX5.3 dayLight,120 degree beam angle bulbs. Both bulbs were used in new light fittings in my bathroom and had received average use for three persons living in the house and using the bathroom. They were never left on when the bathroom was unoccupied. Also present on the same light switch (not of course on the 12v circuit) is a circular fluorescent light. All three lights were brand new and installed when my house was rewired in October 2011. One of the LED bulbs started to flicker on and off after just under two years use and had to be replaced. I reported the incident to the supplier and asked for their comments. Despite a chaser email they have failed to respond at all. The other LED bulb and the fluorescent light are still working fine.

Jeremy Head says:
26 January 2014

We recently had our house completely rewired and all light sockets now take LED bulbs. They have been utterly hopeless. Of 35 bulbs thoughout the house I’d say we replaced at least 10 within 6 months and a further 8 with in 18 months. Tried two different brands and different light temperature too. Our electrician has so far replaced them for free and sends the old ones back as they come with a ‘2 year guarantee’. Some just die, others start to strobe and flicker and then die. Interestingly we also had 6 attached to the same circuit as an old style flourescent tube (in the attic) and every time we turned this light off it blew several of the LED bulbs in the attic bedroom next door if they were alight. Electrician checked to see if there were any issues with having them on the same circuit but there aren’t officially. He ended up rewiring in the attic to put them on different circuits. Happy to supply further details of bulb type and manufacturer if you want them.

Older designs of fluorescent light fittings use a choke to limit the current through the lamp. This generates a high voltage (back emf) when the supply is removed. This high voltage is used to initiate the current flow through the gas in the tube. Any well designed electronic equipment, including your LEDs, should be designed to cope with voltage spikes in the mains.

Motors are another cause of voltage spikes, so a vacuum cleaner or washing machine could also kill LEDs that are not properly protected.

Modern designs of fluorescent light fittings with electronic rather than choke ballast should not produce large voltage spikes. They will be much lighter in weight and will not contain a ‘starter switch’.

David Page says:
27 January 2014

We bought a dimmable LED GLS 14WBC Crompton light bulb about four weeks ago ( 25,000 hr): it has now stopped working – gives a brief flash and then goes out. Pity, while it was working it gave a good light

David, have you checked that the minimum load your dimmer requires to operate correctly does not exceed your total LED wattage(s)?

Nick C says:
27 January 2014

I think you meant to say something like “Have you checked that the total LED wattage exceeds the minimum load your dimmer requires to operate”. I agree with your point though – I have had problems with non-mechanical timers in this way, where the power of the low-energy bulbs connected to them is below the minimum load required for the device to switch off completely.

Nick C, no, I meant to say what I said. If the minimum load your dimmer requires to operate correctly is higher than the LED load then it may cause a problem. The other way round is the same thing – you need a total LED load higher than the minimum required by the dimmer. Take your pick! 🙂

Steve Rennett says:
27 January 2014

I have been using LEDs fr some four years now and the earlier ones are just begining to fail.
Until recently used GU10 downlights in the kitchen with temperature of 5000 k
The more upto date ones now have a spread of 60 degrees and these seem better.
Just recently have purchased B22 fittings to use in the lounge 5000k was too cold and I later found daylight were better#
Have mainly used the internet with no complaints

These have been a major reason for my electricity consumptionl coming down by 400kw pa

Mark Edgar says:
27 January 2014

Amazon are selling LED bulbs from China with a CE safety mark on them.


They can kill you with no protection from contact with the 240V electric circuit.

Amazon say they are not legally responsible again, as they are a shop for others.

Where is the VAT i am paying going?
They take VAT from me in Scotland and then keep it?

MAFIA was taken down due to TAX fraud, why not get Amazon with VAT fraud?

What on earth makes you think that Amazon don’t pass on vat to the Treasury?

Nick C says:
27 January 2014

Not sure what you’re getting at here. What does VAT have to do with CE marking?

Also, which specific LED bulbs are you talking about that can kill you? It may have escaped your attention that old-fashioned bulbs also run on 240v. The reason they are safe is that the design of the bulb ensures that the electrical circuitry is contained within the enclosure of the bulb, protecting people from coming into contact with any live parts, and this is exactly the same for LED bulbs.


The mains wiring is exposed on the outside. The CE mark is not an EU one, it just indicates being made in China.

Looking at the youtube test, if we have seen the same one the corn cob lamp has what to me is clearly a CE mark. You cannot stop this sort of illicit acticity unless you punish the vendors – in the case of Amazon I presume they arer 3rd party sellers who, if the are in Europe, could be prosecuted. I imagine Amazon would regard the posting on their site as an advertisement and thus escape any responsibility.

darell says:
28 January 2014

I had my bathroom renovated in May 2013 with new recessed lights in the ceiling. After 4 months 3 had burned out despite the makers claim that their life was 50000 hours. At £17.50 per bulb these are very expensive. The bulbs are made by Aurora ref AU-DGU1060W/40. Avoid at all cost.

Slavman says:
28 January 2014

All GU10. Bought 8 Auraglow and 6 failed within a year, mostly replaced by Auroglow or refunded by Amazon. Replaced with Kosnic a year ago, no failures yet.

R Moreton says:
28 January 2014

I refurbished my home 2 years ago including a new rewire and replaced the lighting with LED bulbs in the kitchen, bathrooms, hall and landing. So far I have had 8 LED bulbs stop from 13 months until now working despite the supposed cost benefits and long life claimed. We are a working family and therefore only have the lights on for 45 minutes each morning and in the kitchen and bathrooms ac couple of hours per evening maximum. When I contacted the manufacturer SENSIO they refused to acknowledge a problem and stated that the warranty was only for 6 months. Given the cost to replace this has made a mockery of the supposed benefits.

Fred says:
29 January 2014

At the end of October I bought two sets of GU10 LEDs from Amazon:
3 of Philips CorePro CLEDS2WGU1030ND GU10 2-35 Watt LED Bulb
4 of Long Life Lamp Company GU10 5 Watt Super Bright LED with New Chip Technology, Warm White 50w replacements
2 of the Philips LEDs have failed already (end of January) having had normal usage only in a kitchen.
Amazon have agreed to refund the cost of the items.
The Long Life LEDs are fine, as one would hope and expect after so short a period.

Fred, would be worth reporting this to Philips as well as your retailer. Try this link:

A little off-topic, but anyone considering fitting LED replacement tubes in small fluorescent fittings should read this article about potential hazards: http://www.esc.org.uk/fileadmin/user_upload/documents/industry/SwitchedOn-25-Locked_2.pdf

S.Lawson says:
30 January 2014

I bought Aurora GU 10 (PAR 16 – 6W) LEDS. On the package it states lifetime of 30,000 hours. I installed 10 in total. 1 failed just after the 12 month mark and the second at the 13 month mark. The first was replaced by the seller on Amazon (not the manufacturer) as a goodwill gesture- but the second has not as out of warrantee. I did write to customer services at Aurora but have had no reply.

There are at least a dozen named manufacturers / suppliers of LEDs here where failures have been reported, and more that are un-named. The EC have investigated 167 (if I remember correctly) suppliers of whom only 17% met EC requirements on supporting their products with CE marking and appropriate documentation – which suggests they may well be deficient in other respects. So this is a lottery. We don’t have information on why they fail – they may be in unsuitable lights, or poor quality, or defective batches. What is needed, I think, is for life-testing to be reported on a core group of products as a start – I suggest the mainstream manufacturers and suppliers with technical back up and reputations at stake. Then we can begin to buy with a bit more confidence. The hundreds of other suppliers will be the gamble, if we choose to use them.

C V Horie says:
30 January 2014

Once again, Which has not looked at all the important aspects of the light which light bulbs produce. These new technology lamps, fluorescent, sodium street lamps, compact fluorescent, LEDs etc have to be tuned to match natural light sources, such as the sun, blue sky or candles. Otherwise the light seems peculiar.
Their review of the LED bulbs misses out at least two important aspects of light:
the colour temperature from warm (2300 K) to cold (6500 K), measured as the correlated colour temperature CCT;
the colour quality, how well the light matches “natural” light, measured as the colour rendering index CRI 0-100.
Which’s LED review provided no information on either quality of light. The CCT of commercially available LEDs can vary from 2300 K (yellowish light) to ca 5000 K (bluish light). The CRI can vary from nearly 0 (the coloured lamps seen in Christmas tree decoration) to ca 80, about the same as the compact fluorescents. It is of course quite possible to make lamps (LEDS and compact fluorescents) of higher quality than this and they are available in the USA. But the energy saving lamps made available in the UK consistently provide poor quality light because neither the government nor consumer organisations are worried about the effect of light on people. I would not have a lamp with CRI <90 in any living space – it lowers the quality of light and living subconsciously.

The CRI (Ra) is not a perfect measure of the ability of light sources to render colours accurately, and is being researched. However, it is generally accepted that Ra >90 are required for tasks where colour matching is important, and >80 for good quality general lighting. Most people are happy with light of this quality. LEDs, compact fluorescent, tubular fluorescent, certain metal halide, halogens, are all available with Ra>80 from good manufacturers and would be very suitable for home use, as they have colour temperatures of 2700 to 3000. This information is provided by good manufacturers – presumably Which? could include this where it is available. One of the things we are very sensitive to is the way lamps render the colour of skin tones – easy to spot a poor lamp by putting one hand under it and the other under a tungsten lamp at the same time.

I believe that most people are more concerned about cost, operating cost and longevity of lamps.

My impression is that lamps with a higher colour temperature are becoming more popular and I expect that those who have lived with CFLs and LEDs for a few years might find the light produced by incandescent lights a bit strange.

I certainly believe that all lamps should show colour temperature on the packaging and this should be mentioned in reviews. I looked into CRI when CFLs were becoming popular and discovered that not everyone agrees about its significance. The public have lumens and colour temperature to cope with, and anyone interested in CRI can get this information from the manufacturer if they need it.

Colour rendering is not something the consumer will normally think about until they experience poor quality lamps; they have been brought up with, and take for granted, the excellent colour rendering of tungsten lamps. It is one of the key qualities of a lamp, particularly in the home – complaints about colour have been made elsewhere, and this often relates to colour rendering as well as colour appearance. At relatively low lighting levels (as often in the home) warmer colour temperature lamps are generally preferred – typically 2700 – 3500. At higher lighting levels cooler appearance lamps become more acceptable. But whatever the colour temperature, colour rendering is an important quality that we may not always identify. The problem with LEDs is that higher colour temperatures generally produce more light, and these can have fairly dismal colour properties – like the cold purple-blue lamps sold cheaply. So they are often promoted at the expense of the less efficient, but pleasanter, lower temperature whites.

It is early days and I expect that we will see considerable improvement in LED lamps. I will wait until this happens before spending my money.

Like incandescent lamps LEDs produce a continuous spectrum, in contrast to fluorescent lamps. There is the opportunity to build lamps with different types of LED chips to help tailor the light to our requirements.

In future we can expect control of our lighting. An earlier Conversation mentioned the Philips Hue system, controlled by smartphone. That’s a bit like an expensive concept car in my view, but gives an indication of what might be available and affordable before long. We live in exciting times.

“Like incandescent lamps LEDs produce a continuous spectrum”. This is not really true. LEDs are monochromatic devices (strong colours) which is why are so useful for indicator and signal lamps, for example. They do not produce white light. To do this, currently, take a blue InGaN LED and overlay it with a yellowish phosphor that converts some of the blue. This produces a strong blue spike at around 450nm, and a broader emission from the phosphor that peaks around 570nm. The eye is good at combining these together to sense white light, but it does not match the true continuous spectrum of incandescent lamps. Fluorescent lamps use a combination of phosphors to convert UV produced in the lamp into light – they usually have around 7 peaks at different wavelengths superimposed on a more continuous spectrum – again the eye sees these as combining into white and giving generally good colour rendition.

I think it was you who introduced me to how white LEDs work, Malcolm, so I should have been more careful. I should have made a more guarded statement, but this is a public forum. I appreciate that LEDs don’t produce a true continuous spectrum, but I was not able to discern any emission bands with a hand spectroscope, in contrast to the strong bands seen with fluorescent tubes and CFLs.

I expect that LEDs will improve with respect to the quality of light, but for the present, cost and reliability are my main concerns.

Brian says:
30 January 2014

The report in February Which does not say which models by TCP or Ikea have failed. I’d like to know as I’d expect to be able to take them back to be exchanged for new ones.

It is a pity the unreliable lamps were not shown as Don’t Buys so that readers know to avoid them. However, if you have these lamps and they are still working I would not expect a retailer to swap them, even if they might see them again once they do die.

We seem to have drifted away from the reliability issue a bit. Having said that I rejected my last batch of replacement LEDS because they were a rather nasty pale yellow orange, and not the cool white of the originals.
Can someone tell me what effect on colour temperature dimmers have on LEDS? With tungsten filament lamps the hotter the filament the higher the colour temperature, so dimming warms up the light, i.e. lowers the colour temperature. Does this happen at all with LEDS? Also dimming a filament lamp (with a well designed dimmer) prolongs its life. How is a LED affected?

The change in colour temperature is not significant with LEDs, though lamps that allow colour temperature to be varied are in development.

Dimmers used for incandescent lamps are described as ‘leading edge’ dimmers, whereas ‘trailing edge’ dimmers are often recommended for LED lamps. These terms may be used, or the dimmer may simply described as LED-compatible. The dimmer instructions will specify the minimum and maximum number of LEDs it can control. LEDs differ and it is important to follow the advice on whether they can be dimmed or not, and what sort of dimmer to use.

I have not seen information about the effect of dimming on the life of LEDs but on the basis that heat generation seems to be a cause of premature failure, dimming could help to preserve their life.

Two methods of dimming LEDs – current reduction, and pulse width modulation (PWM) at constant current (switching the LED on and off rapidly so the eye does not notice). There is conflicting information, but it seems that with current dimming the LED becomes slightly more yellow as it is reduced, and more blue as it is increased. I suspect that in a domestic installation this is not going to be a significant effect. PWM is stated as not having as much effect.
Generally, life (and efficacy) is improved when dimmed. Does anyone know more about this?

The dimmers I mentioned adjust the proportion of the AC waveform used to power the lamp rather than controlling the current.

Pulse width modulation dimmers are relatively uncommon for domestic applications in the UK, but are best used only if recommended by the lamp manufacturer.

The question of change in LED chip characteristics depends upon the mechanism used by the LED driver (either separate or integral electronics) to perform dimming; this can be typically by controlling the current (which can change junction temperature and shift the wavelenght) or by PWM – rapid on-off switching – (which is said to be less likely to shift the wavelength). The “dimmer switch” feeds this driver but does not directly control the LED chip.

See my recent posting about TCP bulbs and dimmers. I was using the “training edge” dimmer, which I bought specifically as it was supposed to be suitable for LEDs.

I don’t see anything wrong with wrong with my response to Brian, and as you have said there is conflicting information. Compared with incandescent lighting, dimming domestic LEDs does not produce much of a change in colour temperature.

I am interested in technical discussion, having designed and built power control circuitry including dimmers and covered subjects such as PWM in lectures to masters students.

The point I was making is that the dimmer switch on the wall does not directly dim the lamp – it controls the lamp driver circuitry. This driver then either alters the lamp current, or uses PWM. In domestic circuits it is usually current control I imagine. The changes in LED characteristics either way will be unlikely to be significant for domestic lighting. With cheap LEDs there is likely to be much more variation in the white appearance between individual LEDs because of lower quality.

I appreciate this, but is there any evidence that even cheap LED lamps – which seem quite popular – show any significant difference in colour temperature as the are dimmed? I feel that this would be well documented if it was a problem.

The effect seems to centre largely around the shift in blue wavelength, which is dependent upon the LED junction temperature. Perhaps cheap LEDs that run very hot may, in principle, have a bigger change when dimmed – running cooler – than higher quality LEDs. I doubt it would be of any consequence in practice – certainly not compared to dimmed incandescents. It would be interesting to hear whether anyone has noticed a change.

I bought some TCP E27 LEDs, advertised on the box as dimmable, although the small multi-lingual print on the box says “not suitable for dimmers”.

As they were insufficiently bright I fitted two bulbs in each lampholder, using the kind of adaptor that used once to be sold in the UK but which is now unavailable unless you do as I did and buy some in Canada.

The bulbs worked well and dimmed properly once I had installed the correct kind of dimmer, but began to fail after about 1000 hours of use. The retailer, Burton & Sons, replaced the bulbs as they failed without demur, but, of course, I had to pay for the postage and packing and put up with the inconvenience of trekking to the post office each time.

Burton suggested that the failures were due my electrical installation or maybe a voltage spike but, in truth, my installation is a normal one and voltage spikes, if they happen, have never caused failures of other kinds of bulbs (or any other equipment).

I still have the last set of four replacement bulbs (which I received in August 2012) as I didn’t want to risk installing them and am using normal CFLs (without using the dimmer, of course)

It might be that using the dimmer caused the problem since, I confess, I only saw the caveat about dimmer unsuitability in the very small print a few minutes ago when checking the details of the bulbs. Previously I had relied on the retailer’s description of the bulbs as “dimmable”, the legend on the box that says “dimmable” and the legend in the specification that says, “Can be used with dimmers”. If these bulbs are genuinely unsuitable for use with dimmers then clearly they are being sold for a purpose for which they are not suited.

I will probably contact Burton and Sons and see what they have to say.

My last comment relates to Malcolm’s post.

Perhaps we should be investigating the contribution of voltage spikes as a cause of failure of LED lamps. I am familiar with the problems of using LED lamps off-grid in applications such as boats and RVs, where the supply is a 12 or 24 V battery bank charged by an alternator. Over-voltage (modern alternators charge 12 V battery banks at approaching 15 V) has been addressed and specialist suppliers sell LED lamps capable of operating at up to 30 V, but some lamps are much more readily damaged by voltage spikes in the supply.

I will look through the literature when I have but perhaps Richard has already looked into this.

In considering the effect of voltage spikes it is probably worth considering 230 V and 12 V LED lamps separately, since in the latter case the lamp may be protected by virtue of the power supply provided to decrease the voltage.