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Circa 2012, I bought an IKEA "Stockholm" LED floor lamp (product info). Its bulb recently burnt out.1 While the product was advertised as non-serviceable, I disassembled the lamp. The lamp's components seem straightforward, except for the heatsink.

The product features a large aluminum heatsink (approx. 3" diameter, 1.5" deep) around the LED bulb. (The lightbulb looks to be PAR16.)

Heatsink front view

Heatsink side view

dissassembled lamp head

My question is: In repairing this lamp, do I need to replace the heatsink or do newer LED lightbulbs not require an external heatsink? The product's heatsink was glued (or otherwise permanently affixed) to the now-dead bulb, and it seems like I'll have a lot of trouble finding a replacement part.


1 While its light bulb was estimated to last 20,000 hours, I suspect it lasted less than a tenth of that.

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    disassembled - with a can opener, by the looks of this ;-) ! – Ecnerwal May 2 '17 at 12:58
  • @Ecnerwal Painstakingly, using wire cutters and pliers, actually. 😂 I wanted to ensure there was no way to separate the heatsink. But I'm now certain that the heatsink, the bulb, and the reflector were all glued together. – Jacob Budin May 2 '17 at 14:13
  • @Ecnerwal That's what it looks like when you disassemble an LED. I have a Lights of America LED that lasted 2 years and those are about my prospects for owning it. – Harper - Reinstate Monica May 2 '17 at 15:03
  • @JacobBudin - given the pictures of the lamp design - the heat sink is most probably required for any LED lamp bright enough for it. See my answer .. – Ken May 2 '17 at 17:37
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Edit: Now you've posted more pictures, I see what you're doing. Let's take a look at your presumptions here:

  • Anything that makes light must surely have a "bulb" of some kind.
  • The bulb is fragile by nature, and it will inevitably burn out.
  • When a lamp fails, it's almost always the bulb burning out.
  • Scrapping a fixture when a bulb burns out is insane; it must be replaceable somehow.
  • If a manufacturer says it's not replaceable, that can't possibly be true.

All those presumptions are dead wrong with LEDs.

That is a packaged consumer product with a permanently mounted LED in it. It contains several components, including packaging, a power supply which converts AC into the constant-current the LEDs need, a beefy heat sink, the LED emitters proper, and lensing to direct the light.

Yes, you need heatsinks

LED emitters used for illumination make a lot of heat. Some is from the LED itself, and that is decided by how hard the LED is driven. Some is from the inherently inefficient phosphors which change blue light into spectral light.

LEDs are much more efficient than the old incandescents, but even so, almost all the watts of energy put into an LED emitter turns into heat, not light. That means the heat sink must be rated for the wattage of the LED. The LED wants to be kept as cool as possible, and the cooler it is kept, the better it will run. But you're still going to have a lot of heat.

There is basically no way an LED of any brightness is going to function for long without a heat sink.

So why do they fail?

Properly cooled, an LED emtter is likely to outlive all of us. If there's anywhere cheap builders will cut costs, it'll be in the power supply. This is the part which inputs 120/230V mains voltage and outputs a constant-current DC for the LED emitters proper. Capacitors are the most sensitive component - they ordinarily have a finite service life, and you have to go out of your way to spec the really good ones or spend a bit more on a capacitorless design. The top failure points are:

  • Power supply (particularly capacitors)
  • Lamp wiring
  • Environment damage
  • LED coming unglued from the heat sink, causing overheat
  • Blockage of airflow to the heat sink
  • Lead-free RoHS solder crystallizing over years - reflow the solder or use lead solder
  • Lenses fogging up or discoloring
  • Cheaper LED emitters getting dim as they age

The LED emitter is rather unlikely to fail. What does this mean for fixture manufacturers? It means making LEDs removable is a waste of time and actually makes the product less reliable, because a socket problem is more likely than an LED emitter problem.

With the very concept of a "bulb" gone, it gives the manufacturer freedom to design fixtures as they please.

This means you were barking up the wrong tree when you took it apart trying to find the mystery replaceable bulb. There was probably nothing wrong with the emitters proper, unless they came unglued from the heat sink. Given the age, most likely it was a power supply problem. You could have tested for this with a voltmeter.

More about overdriving LEDs

LED emitters (the chip inside the "bulb" product) are expensive, a common cost-cutting approach is to overdrive LEDs. The manufacturers fully expect this and spec the LEDs for this. For instance this Cree XP-G2 is rated at 1500ma but is specced at 350ma. Notice most of the charts assume 350ma, or assume 85C.

This unit (in R4 code, nominal 130lm) produces at 85C (and you can follow along on page 11, electrical characteristics and relative flux vs. current charts):

  • At 350ma, voltage is 2.8, watts are 0.98, lumens are 100% or 130, lm/w is 133.
  • At 750ma, voltage is 2.93, watts are 2.20, lumens are 195% or 253.5, lm/w is 115.
  • At 1125ma, voltage is 3.05, watts are 3.43, lumens are 270% or 351, lm/w is 102.
  • At 1500ma, voltage is 3.14, watts are 4.71, lumens are 340% or 442, lm/w is 94.

This assumes 85C. Go to page 10 and you can see exactly how cooler temperatures result in more light; 10% more at 25C, and 10% less at 125C. Now look at thermal design on page 13 and you'll see where the device requires a derate for high currents at high temperatures.

Lamp manufacturers balance the cost of more emitters (to run more efficiently) versus bigger heatsinks on fewer emitters. Generally they need a heatsink regardless, so making a somewhat bigger heat sink is the cheapest option.

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  • your statement "A perfect light source is 683 lumens/watt" I find completely inaccurate if I get 1 million lumens per watt - I am merely more efficient. – Ken May 2 '17 at 17:24
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    @Ken If you get 1 million lumens per watt, you have altered the laws of physics. I am sorry, but you simply don't know what you're talking about. I didn't pull 683 lm/w out of my hat, it is a definitive number and you should research what that's all about. – Harper - Reinstate Monica May 2 '17 at 17:35
  • theoretical mappings of how bright to the human eye a candle is comparatively to an artificial light source is not the physics defining it as to what is considered 100% efficient (it is theoretical) but it has to do with the ability of the human eye to see x amount (that is not an electrical characteristic but a physical one) - so I will apologize if I have offended you. – Ken May 2 '17 at 18:08
  • @Ken I am offended only by idiocy and I recognize it can sometimes conceal genius. The problem is that what you're saying does not map to the common and generally accepted understanding of the field. If your understanding of the field is extraordinary, then extraordinary claims require extraordinary proofs. Please provide references for everything you say. If the 600-character comments section is too compressed for that, consider writing an Answer. – Harper - Reinstate Monica May 2 '17 at 19:04
  • @Harper Thanks for the edit. "Given the age, most likely it was a power supply problem." Yes. This was the issue. Hopefully someone will learn from my mistake. – Jacob Budin May 3 '17 at 16:01
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That depends entirely on the "bulb" - given that you are basically rebuilding the "non-servicable" lamp, your bulb (or light source) choice will vary.

Observationally, despite its large size, evidence (the short lifespan) would suggest that the overall design of the lamp may not promote adequate cooling, since excessive heat is by far the major cause of short lifetimes for LED lamps and their drivers. Lack of airflow or other poor thermal design might have done this one in.

My overall experience is that "LED Bulbs" appear to generally give poorer service than LED fixtures designed for LEDs from the ground up. You might call this the worst of both worlds, as it's non-servicable (like most from the ground up designs) but uses a bulb-style light source. But if you are retrofitting with a "lightbulb" type LED, whatever heatsink it needs should be built into the bulb (which is a big reason bulb-types are compromised - "bulb shapes" often don't allow for adequate heatsinking.) You do need to allow for adequate airflow around the bulb (which is how a lot of LED bulbs get killed even if they are well designed - folks ignore the bit about not putting them in enclosed fixtures.)

Several of the newer designs have managed to reduce the waste heat and generally do better thermal management despite the constraints of the bulb shape - but I would suggest going for a "full sized" bulb if possible and going with a bulb. If you split it up into a driver and LEDs as separate entities, there are a few more options, but that's more of an electronics hobby than most folks care to tackle in a lamp repair.

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  • Is it the bulb itself or the other internal wiring to convert the 120v AC to a usable digital current for the LEDs that generates the heat? – The Evil Greebo May 2 '17 at 13:46
  • Both - and when the two are in close proximity cooling is more complicated. But even with the driver electronics separated at some distance, a high-intensity LED puts out a lot of heat, and much of (good) LED fixture design is thermal design to deal with that and prevent the LED from destructively overheating. – Ecnerwal May 2 '17 at 13:57
  • @Ecnerwal The power supply is external and attached to the AC plug. (I was, of course, hoping not to have to replace it.) Also: "going with a ___ bulb" Were you going to write CFL? Thank you. – Jacob Budin May 2 '17 at 14:18
  • No - I despise CFLs and was referring to an LED replacement bulb - i.e. the sort of thing that screws into a socket at mains voltage and has the conversion electronics built in. Since you have and would like to re-use the external supply - Step zero - have you actually checked that the power supply is working? Your lamp failure could be the LED, could be the power supply. Step one - determine its parameters (voltage, current, and which one of those does it primarily control?.) Step two - go shopping for LEDs that match the parameters found in step one. – Ecnerwal May 2 '17 at 14:25
  • @Ecnerwal cooling matters to an LED, but that is often the fault of the fixture's design. A few fixtures are designed to be E-Z-Bake ovens basically, aiming to keep the incandescent bulb nice and hot (for what? Efficiency?) The #1 killer of LEDs is buying cheap Cheese. The only thing that annoys me more than an "incandescents out of my cold dead hands" curmudgeon is the skinflint "I bought a dollar-store junk brand of of X technology, and it failed, therefore all X technology is bad". Not that Ikea is junk, I find it to be better than the price would suggest. – Harper - Reinstate Monica May 2 '17 at 15:01
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You stated that the bulb looks to be PAR16 - assuming you are correct - which I am suspecting you might be as some manufacturers do utilize POTS components to produce a product - and looking at that crazy lamp I would say in your case is a good possibility - however I can not see all of it like you can.

You will need the Heat Sink in this case - the heat sink is additional cooling given the confined space of that lamp assembly. The "Glue" that holds it together is not a standard glue either - it is a special epoxy that allows for the conduction of heat to transfer.

Now if it is not a par 16 but a specially made unit - you would need to order the part from the manufacturer - they will most likely not sell just the lamp itself but also require the heatsink as I said the glue is not glue but special epoxy.

Hope that helps you.

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  • Thanks. Unfortunately, I cannot order replacement parts for this lamp (IKEA has discontinued the model I own), and I'm not aware of any supplier who sells these kinds of components. Is it your opinion I should throw it away then? – Jacob Budin May 2 '17 at 22:54
  • @JacobBudin my experience has always been this - it costs me more in the end to do this than to buy a new one. Some Items I am really attached to - I like the design, the function etc.. and when it breaks I like to do what you are attempting. When parts are available anywhere - it works (still a bit more expensive but you know kind of attached to the thing), but when I have to re-engineer and place non standard parts usually it not only costs a lot more but does not have the 'finished' look anymore.Unless I can source the parts I would buy new; It really is a personal decision though. – Ken May 3 '17 at 22:52

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