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Domestic LED lamps: reliability

  1. Nov 23, 2012 #1

    sophiecentaur

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    I have bought just four mains voltage LED lamps, in my life. Three of them have failed. One has failed after only a very few months and is being replaced by the supplier. They claim that these expensive items are supposed to last for tens of thousands of hours. Has anyone else had this problem or have I just been very unlucky?
    The two GU10 lamps both have two burned out (?) diodes in them - two elements are brown!.
    At a tenner a time, I just wonder whether they are a step too far, too fast for this technology. Or could they just be bad counterfeits?
     
  2. jcsd
  3. Nov 23, 2012 #2
    Fluorescent "saving" lamps lose their brightness quickly. Not tried Led up to now.

    Professional signalling Led have a limited lifetime guaranteed at just about 1 year permanent use; improving it is difficult because of the high current density needed for efficiency - if not, recombination is essentially non-radiative.

    Led used for lighting may perfectly be boosted and badly manufactured, since cost is the very limiting factor in this use, so I would expect bad reliability and counterfeits. Add to it that white Led use GaN which is a newer technology than GaP.
     
  4. Nov 23, 2012 #3
    If CFLs are indeed losing brightness faster than LED bulbs then that would be the only reason to switch. In my (not so thorough) research I failed to see any other advantage. Also when comparing bulbs side by side in stores, I can never find a LED with better stats than the best CFL they have, in terms of lm/W & stuff. And that best CFL is always cheaper, 3 to 10 times usually.
     
  5. Nov 24, 2012 #4

    sophiecentaur

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    But the reliability is absolute pants imo. Have I just been unlucky in that respect?
     
  6. Nov 24, 2012 #5
    Thermal management is the key to both LED and CFL life - are you using them in High Hats ( ceiling mounted cans?) or in an open fixture?
     
  7. Nov 24, 2012 #6

    AlephZero

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    The same applied to incandescent lights as well.

    I used to have one light socket in my house that seemed to "burn up" incandescent bulbs faster than aoy others. Eventually, I couldn't get a blown bulb out of the socket because the spring-loaded pins had apparently seized up. Taking the socket off the ceiling I found one of the supply wires had never been tightened properly, and presumably the high resistance joint had been generating heat, since the back of the socket was covered in "burnt-on" gunk that had seized up the pins.

    After replacing the socket, no more blown bulbs!
     
  8. Nov 24, 2012 #7

    sophiecentaur

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    I've come across this sort of thing before with incandescents and I have always understood it can be due to thermal cycling with to an intermittent connection. With an LED lamp, the losses in an HR joint can't be very much.

    @Windadct
    The GU10s were in a ceiling fitting. It never got more than 'detectably warm'; never anything like 'hand hot'.
     
  9. Nov 24, 2012 #8

    uart

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    By coincidence that's the exact same number of I have. The ones I have are for direct replacement of a standard 240 volt bayonet cap fitting. Mine have only been running for a few months, but no failures yet.

    I did notice, when I was looking at what to buy, that some lamps specifically warned that they were not suitable for fully enclosed fittings. I think windadct is correct about thermal conditions being critical. The problem with LED's is that the light (and heat) is all produced from a relatively small area, so more concentrated than a CFL. Also, being a semiconductor, it's obviously much more sensitive to heat than something like a tungsten filament (sorry, I know I didn't need to tell you that :redface:). Anyway, the upshot I think is, that the actual LED devices can get too hot even when the overall fitting doesn't feel particularly hot.

    I know LED mains lamps are still rapidly developing in terms of lumens/watt and performance/price in general. Perhaps they've still got a way to go in terms of thermal reliability as well. We're just coming into summer here, so I'll probably find out soon if mine are going to survive ok in the fittings in which they're installed.
     
  10. Nov 24, 2012 #9

    uart

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    This is not something that's static though. It's a bit like the famous study in the 1950's that predicted the world-wide demand for computers as being "approximately six". :biggrin:

    LED's are definitely improving in terms of watts/lumen, and the prices will fall dramatically in the not too distant future too. Currently the LED lamps that I have are about 1/2 to 2/3rds of the power consumption of equivalent CFLs.

    With rising electricity prices, don't underestimate the ability of even modest energy savings to offset the lamp's cost. I'm paying 25c/kWh for electricity, so even a 5W energy saving will pay for the extra price many times over during their expected lifetime.
     
  11. Nov 25, 2012 #10

    jim hardy

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    Do they run hot to the touch?

    I'd wager it's some part not holding up to the voltage stress.

    Can you cut one open?
    If there's inductors and IC's then it probably has one of those complex power factor correcting circuits,,

    and i'd wager that particular manufacturer is stumbling up the learning curve.

    that's just a guess......

    old jim
     
  12. Nov 25, 2012 #11
    The CFLs and LED put out much less heat - and are thus much more efficient. However they do not need to run too hot to age prematurely, so when they are confined in a can they run hotter then their spec. and die early. Some CFLs are now rated for this use - I have them last a little longer than the incandescents - but they cost more etc. The bulk of engineering in the LEDs market today is all in thermal management.
    Another point to be made to the efficiency - if you are cooling your home, with an incandescent you are paying more for the higher energy use and then you have to pay to remove the heat with your AC - there is a double whammy. If you heat your home you do get some "value" from the wasted heat - and if you heat with electric heaters ( not heat pumps) - the cost is the same with a heater element or a lightbub - but in a ceiling fixture - that heat may just be going into the attic...My point being that these the choice is not always clear cut, I use both. I have also found that the CFLs - are good for drop & portable lights - they are mechanically more durable, don't die it you bump on while on / hot, and they do not get as how so they do not burn you when you work around the lamp. There are also some higher power ones that can put out more light then the incandescent in the same socket, 200W equivalent CFL put out a lot of light, and runs on 42W.
    IMO - the LEDs are not ready for prime time - in some commercial and industrial applications they make sense - but I have not see a general purpose one that is worth the $.
     
    Last edited: Nov 25, 2012
  13. Nov 25, 2012 #12

    sophiecentaur

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    Very likely. And I am (we all are) paying for their testing programme. Give it a few years and we'll wonder why we ever used incandescents or even CFLs - just like those poor old CRTs. When you think of the incredible powers that solid state devices can handle these days, it really has to be only a matter of time.

    In the GU10's there are single elements with that 'burned out', brown look. I think there must be a power sharing problem with these multi LED arrays - which is probably why it's such a big deal to get dimmable ones. I wonder if they are just 'selected' off the production line.
     
  14. Nov 25, 2012 #13
    Cripes! I've never thought about it this way. So in an incandescent bulb we have a great durable device capable of producing both light and heat and it costs less than its individual heating and illuminating counterparts with the same specs.

    A 2000W heater costs more than 20 100W bulbs and it does not produce any light. It is also possible that it won't outlive the light bulbs. If I install enough incandescents I will have light and pretty much the same amount of heat as most light will turn into heat when absorbed by the walls.

    If I line up the walls with solar panels I can even have some of the electricity back by preventing the light from becoming heat. Banning these types of light bulbs in cold climates seems a bit contra-intuitive.
     
  15. Nov 25, 2012 #14

    jim hardy

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  16. Nov 25, 2012 #15

    uart

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    As already pointed out by Windadct, incandescent lights are not particularly good as heaters because of their placement, with a large percentage of the heat going straight into the roof space. Also sometime you want the heat and not the light, and sometimes vice versa.

    You can get special purpose light/heater combination lamps that are designed project the infra-red downward. They used to be fairly popular here for bathroom heating a while back.
     
  17. Nov 26, 2012 #16

    sophiecentaur

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    It's a fairly safe bet that a heater element, operating at a few hundred degrees C will last a lot longer than an incandescent filament. Oil filled radiator heaters hardly exceed 100C.

    There isn't a lot to recommend filament lamps except for the fact that the colour of their light is nicer - largely because we're used to it, I think.

    Unwanted heat, produced by electrical equipment seems to get a lot of attention on these fora. Why doesn't someone start a thread which sings the praises of wearing thick clothing indoors and turning the heating off / down? Now that makes really good sense (he said, in his T Shirt and Jeans).
     
  18. Nov 26, 2012 #17

    jim hardy

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    there's aplace for everything.

    I put the fourescent one in all the ceiling fixtures because it reduces the frequency of replacing them. And thy're nice for shop worklights, as s omebody else noted.

    But for reading on winter nights i really like an incandescent table lamp, especially with a touch-dimmer installed. And i use them with a dimmer to keep pipes from freezing in outbuildings. I'm about a 50/50 mix in my house..

    So when gov't banned their manufacture i hoarded about 200 of them.

    old jim
     
  19. Nov 27, 2012 #18

    uart

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    Hi Jim, here in Australia they didn't technically ban them, they just set efficiency standards for lighting that the conventional (cheap) incandescent lamps didn't meet. So kind of a de-facto ban.

    It didn't take very long however before manufacturers just started producing more efficient incandescent globes (better gas and/or filament and hotter temperature) to meet the new standards. It wasn't all that huge of an improvement, 60W reduced to about 45W I think, but it was enough apparently. So incandescent light globes are back on the shelves in stores here and very readily available. You should check, they might have done something similar in the US.
     
  20. Nov 27, 2012 #19

    sophiecentaur

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    In Australia they have seen the light, you could say.
     
  21. Nov 27, 2012 #20

    NascentOxygen

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    There are two areas where reliability can suffer: poor quality control of the individual LEDs, and the cheap, badly built transformerless power arrangement that Chinese manufacturers use for the substitute lamp. With multiple LEDs in series to get the required voltage drop, failure of 1 means failure of that whole string.

    An alternative arrangement is to have a separate low voltage transformer in the ceiling, and (for optimal efficiency) operate multiple (2 or 4) LED ceiling lamps from that one transformer. This may be optimal efficiency because a typical LED lamp might be 8W, but the typical mains transformer on light loading has heat losses of around 10W. (So there's a hidden 50% efficiency hit right from the start if you allocate 1 transformer per lamp.)

    Drop-in LED replacements are even available for the long 4' fluro tubes, over $100 each and bristling with LEDs.

    Here's a little light reading (pun intended):
    http://forums.whirlpool.net.au/forum-replies.cfm?t=1905803 [Broken]
    http://forums.whirlpool.net.au/forum-replies.cfm?t=1951172 [Broken]
    http://forums.whirlpool.net.au/forum-replies.cfm?t=1917704 [Broken]
    http://forums.whirlpool.net.au/forum-replies.cfm?t=1499905 [Broken]
    http://forums.whirlpool.net.au/forum-replies.cfm?t=1156179 [Broken]
     
    Last edited by a moderator: May 6, 2017
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