The big lie about LED lighting lifetime

The great LED lightbulb rip-off: One in four expensive ‘long-life’ bulbs doesn’t last anything like as long as the makers claim article tells that many energy-efficient LED light bulbs failed before their advertised lifespan, tests have found. Disappointing result comes despite claims of them lasting 25,000 hours.  The consumer watchdog and European partners tested five samples of 46 types of bulb. LED light bulbs have a tendency to make grand claims about their lifespan, many are failing well before promised lifetime. New EU regulations say that from March 1, 90 per cent of any batch of LED (light emitting diode) bulbs should last at least 6,000 hours.

In The big lie about LED lighting article Scott Elder, principal engineer with Linear Technology discusses why LED lighting fails earlier than consumers might expect. Despite all this investment converting home lighting to LED bulbs, I have yet to experience the primary benefit of long life. Why?  As it turns out, the answer is quite simple. The lifetime is not a function of the LED component itself, but rather the total circuit solution. Virtually everyone who scored the lamp as a one in Amazon.com rating claimed their score was because the lamps failed very quickly.

 LED lamp life expectancy depends on fixture type and usage scenario article tells that typically lamp manufacturer have temperature data to share or  specs on use in enclosures. We learned that no standards exist to test and provide this information, more so that the LED lamp is considered an isolated thermal plane and not considered to dissipate heat into the fixture. Electronics folks know there are no new technical breakthroughs in thermal management. The latest LED lamps run electronics hotter than their predecessors and drivers can fail quickly from de-soldering or thermal breakdown of components.

 

12 Comments

  1. Tomi Engdahl says:

    Hot tips on thermal management for LED lighting
    http://www.edn.com/electronics-blogs/led-zone/4440742/Hot-tips-on-thermal-management-for-LED-lighting?_mc=NL_EDN_EDT_EDN_today_20151105

    Keeping LEDs cool in high-power LED designs can be almost as challenging as keeping them lit. This is especially true with the smaller form factors, increased power densities, and lower thermal resistance packages found in today’s designs.

    Utilizing high power LEDs in commercial lighting applications has increased dramatically over the past few years. Today’s high power designs have advanced to the point where the need for good thermal management solutions is absolutely necessary to assure consistent system performance and long-term reliability.

    variety of highly efficient, flexible, and easy to handle thermally conductive interface materials to meet current and future needs for effectively cooling electronic systems ensuring long term reliability.

    One of those materials is polymer based dispensable gap fillers

    Thermally conductive cure-in-place liquid gap fillers can serve as a practical alternative to classical pads that provide excellent thermal management design and component assembly flexibility.

    Reply
  2. Tomi Engdahl says:

    How long do LEDs really last?
    http://www.edn.com/electronics-blogs/led-zone/4441442/How-long-do-LEDs-really-last-?_mc=NL_EDN_EDT_EDN_weekly_20160218&cid=NL_EDN_EDT_EDN_weekly_20160218&elqTrackId=dcd8f5ac87c8424e89f46087117ef40e&elq=67b4966efe9f430b8e0133b911161c89&elqaid=30892&elqat=1&elqCampaignId=27031

    I was contemplating my own mortality recently, when I realized 2015 passed by in a blur. Ruminating about the loss of yet one more year, I looked at my LED-laden lamp and thought, “Sure, you might last 50,000 hours, while my expiration date is virtually unknown.” But, was this true?

    Happy to take the thought process from my own shelf life to that of an LED, I began to wonder if that 50,000, 35,000, or 25,000 hours of use from an LED could possibly be accurate. For one thing, I don’t mark down the date of purchase for my LEDs. Do you?

    Most important, how do we know these claims are accurate – and then I was off on a research mission.

    A little more than a year ago, the Daily Mail ran an article claiming that 25% of the expensive long-life bulbs came up short on the claims—with some even falling below the European Union’s legal minimum life of 6,000 hours. These were bulbs that claimed between 15,000 and 25,000 hours of use.

    Not a fan of the Daily Mail? What might you believe? The U.S. Department of Energy’s website discusses tests for a variety of bulb types.

    In that vein, how long do you think a bulb claiming 50,000 hours would need to be tested? Try 5.7 years. What it comes down to is that there seem to be no real sure-fire ways to test the long-term performance/viability of the LED.

    According to the DOE, “electrical and thermal design of the LED system or fixture determine how long LEDs will last and how much light they will provide. Driving the LED at higher than rated current will increase relative light output but decrease useful life. Operating the LED at higher than design temperature will also decrease useful life significantly.”

    Reply
  3. Tomi Engdahl says:

    Measurement basics in LED thermal management
    http://www.edn.com/design/led/4442570/Measurement-basics-in-LED-thermal-management-?_mc=NL_EDN_EDT_EDN_today_20160823&cid=NL_EDN_EDT_EDN_today_20160823&elqTrackId=07bb91be332d4689bd3ddc5b2ad6d86b&elq=f0607658a677432eb1e4756293a30f03&elqaid=33551&elqat=1&elqCampaignId=29328

    A successful LED design needs a balance of form and function to be a desirable luminaire with the right lumen output. Sounds simple enough, but these two requirements are often in conflict. When form trumps function, LEDs that are usually mounted onto a metal-clad PCB (MCPCB) as a module are all too often crammed together, creating a module with high-power density. If the device has not been designed to remove the heat from the LEDs effectively, there is a real risk of the LED overheating. As with any semiconductor, when LEDs overheat efficiency is reduced, light quality deteriorates, lifespan shortens and ultimately the LED can catastrophically fail.

    Even with extreme high power density designs, this can be avoided by having a basic understanding of thermal design. However, it can be difficult to unravel the claims made by thermal management suppliers regarding how their materials perform. This can lead poor choices, and in a worst-case scenario overheating or failing, LEDs.

    Three critical factors to consider when looking at the thermal performance are conductivity, interface resistance and impedance, which combine to give the total thermal resistance of the design.

    Fundamentally a good understanding of the measurements involved in LED thermal management (and knowing some of the pratfalls involved) is critical. It can make the difference between a differentiated design that saves money and one that will either be uncompetitive or, in some cases, literally burn itself out.

    Reply
  4. Tomi Engdahl says:

    Cooling high-power LEDs: The four myths about active vs. passive methods
    http://www.edn.com/electronics-blogs/led-insights/4422914/Cooling-high-power-LEDs–The-four-myths-about-active-vs–passive-methods

    In high-power lighting, needs are emerging for LED luminaires rated to 100, 200 or even 600 watts (over 60,000 lumens), to cover wide areas. The higher-power heat sinks increase in size and weight exponentially. The consequence is escalation of costs for tooling, assembly, shipping, and installation.

    It turns out that active cooling (i.e., the use of fan-cooled heat sinks) can exhibit dramatic size, weight and cost reductions at those elevated power levels. A 400-watt, passive-cooled high-bay fixture might weigh 75 pounds and be the size of a two-drawer file cabinet. An active-cooled version might weigh only 15 pounds and be no larger than a pizza box.

    Why would anybody use passive cooling?”… you ask. Often it makes sense. Often it does not.

    While the industry is inexorably embracing active cooling at power levels above 50 watts, there is still resistance in many “old school” quarters.

    Those previously mentioned hundreds of millions of DC ball-bearing brushless fans, operating 24/7 for years, without filters, in Internet and wireless equipment, with no degradation of cooling, are quite a myth-buster all by themselves.

    Reply
  5. Tomi Engdahl says:

    Teardown: What killed this LED bulb?
    http://www.edn.com/design/led/4442724/Teardown–What-killed-this-LED-bulb-?_mc=NL_EDN_EDT_EDN_weekly_20160922&cid=NL_EDN_EDT_EDN_weekly_20160922&elqTrackId=e65272ae7e2f4e40afa5aeb81a4be2d0&elq=4d076a6c73904fc7aac4fe936645df87&elqaid=33988&elqat=1&elqCampaignId=29711

    The market’s matured quite a bit since then, and the technology’s gone mainstream in a big way, thanks in no small part to plummeting prices.

    Any guesses on the failure root cause, readers?

    Reply
  6. Tomi Engdahl says:

    LED bulbs can bring heat
    http://www.edn.com/electronics-blogs/living-analog/4442767/LED-bulbs-can-bring-heat?_mc=NL_EDN_EDT_EDN_analog_20160929&cid=NL_EDN_EDT_EDN_analog_20160929&elqTrackId=6184996e6f4149b6bc190abce9d7e412&elq=1bf46ad9b61843d6bcfb68b829f9bd24&elqaid=34083&elqat=1&elqCampaignId=29794

    I had a CFL fail the other day at our upstate house but when I went to the local hardware store to buy a replacement, there was nothing like it to be found. I did find a light emitting diode (LED)

    The spherical part of the envelope was just moderately warm to the touch but when I moved up the envelope toward the lamp’s base, I started getting burned. High efficiency or not, this thing was running hot so I decided to do some testing.

    The LED bulb is much heavier than the incandescent bulb. Its package cautions you to make sure that your bulb socket can support the heavier weight.

    It has crossed my mind that since the LED bulb has its higher temperature near the base (160°F) and since that base temperature is higher than the base temperature of the incandescent bulb (132°F), the plastic-shelled socket I used might not be a good choice for LED bulb service. Furthermore, although the LED bulb I examined has lower maximum temperatures than that 100 watt incandescent bulb, that 160°F temperature is high enough to do serious harm to unwary fingers!!

    Some of the hype I’ve seen in advertisements for these things includes verbiage about good power efficiency which may lull one into a false sense of security about heating, but rest assured that if you get careless, an LED bulb can burn you.

    Reply
  7. Tomi Engdahl says:

    LED lamp cycles on and off, why?
    http://www.edn.com/electronics-blogs/rowe-s-and-columns/4443011/LED-lamp-cycles-on-and-off–why-

    After using one of the office BR30 LEDs (Feit Electric from Costco) for over a year, I noticed it would cycle on and off every few minutes after about 30 minutes of use. Suspecting a heating problem,

    Sure enough, the LED stays on because the heat was no longer constrained in the recessed fixture. The question is: Why does only one of the LED lamps cycle on and off? Does the heat not properly dissipate? Does the temperature-sensing circuit turn the LEDs off too soon?

    It was time to make some measurements.

    What caused the cycling LED lamp to cycle? There are two likely causes.

    The temperature-measuring circuit caused the lamp to turn off prematurely.
    Insufficient thermal conduction from the LEDs to the heat sink.

    Opening the cycling and good lamps revealed a difference.

    I want to know why this one lamp cycles and how to fix it.

    Suggestions?

    Comments:

    I doubt that there is a temperature sensor. I have taken apart enough LED lights and have never seen any. There might be a chip with built-in overload and overtemperature detection, but I doubt even that.

    More likely the lack of thermal paste has earlier caused an overheating of some of the LEDs on the board. Since all of them are connected in a long series string (you can see that from the traces) a thermal failure in one LED will interrupt the whole chain and give the affected LED time to cool down again.

    vandamme

    I had an LED that cycled on and off. It was a single chip packaged device connected to a USB plug (through a resistor). It worked nicely for my PC keyboard until it started to flash at about a 1-2 Hz rate. The crappy wire bond was being pulled off the chip by thermal expansion.

    Some 20-30 years ago, some manufacturer had a bad run of power transistors with a similar problem, and they got used in small radio audio amplifiers. They would “motorboat” at a few Hertz, which sounded like a power supply problem. I encountered one and after replacing capacitors to no avail, discovered the history.

    Bill_Jaffa

    Amazing how a “simple” apparent thermal-cycling problem can be tough to figure out and get to the root cause. Nice job on the instrumentation and analysis you did!

    Reply
  8. Tomi Engdahl says:

    How long will an LED lamp last?
    http://www.integral-led.com/support/how-long-will-led-lamp-last

    LED lamps have a longer lifespan than conventional filament, halogen and CFL lamps.

    LED lamp rated at 25,000 hours
    As you can see a LED lamp will last over 22 years (at 3 hours per day) against a filament lamp of less than a year and a CFL of just over 9 years.

    All lamps including LED have a number of switching cycles. This is the minimum number of times the bulb can be switched ON and OFF before failure in normal use, lamps may go on to last longer. For a typical value of 12,500 the lamp can be switched ON and OFF once a day for a minimum of 34 years!

    Reply
  9. Tomi Engdahl says:

    Home> Community > Blogs > LED Zone
    LED lighting system reliability: Ensuring a robust design
    http://www.edn.com/electronics-blogs/led-zone/4458687/LED-lighting-system-reliability–Ensuring-a-robust-design

    At least 10 years after they were first applied for general illumination, the subject of how to assess the reliability of LED lighting products is still an on-going subject of debate, and sometimes, confusion. Below you’ll learn about some metrics and processes for reliability designing LED lighting systems.

    The lifetime of incumbent lighting technologies like incandescent or fluorescent lamps is usually characterized by average rated life, which is the time in hours at which half a test population of continuously running lamps fails (i.e., light is no longer emitted). For incandescent lamps, average rated life is about 1,000 hours, for compact fluorescent lamps, about 12,000 hours, and for linear fluorescents, about 25,000 hours. In contrast, LEDs, operating under appropriate environmental conditions can emit light for 100,000 hours or longer, making an average rated life measurement impossible.

    Instead, LED lighting lifetime is characterized using the L70 metric which is the time in hours at which the light output measured in lumens (L) drops to 70% of initial. The shortcoming of L70 from a reliability engineering perspective is that the test methods, published by the recognized authoritative body for lighting, the Illuminating Engineering Society, are based on lumen output measurements for the LED packages only and don’t take other system components such as the driver, thermal management design, and even optics into account. Incumbent lighting manufacturers have not focused heavily on overall system reliability because the lamp is nearly always the first component to fail. With the advent of LED lighting, manufacturers and end-users have come to understand that other parts of the lighting system can be the limiting factor in overall life as the table below illustrates.

    Reliability, in its formal sense, is the probability that a part or system will perform as intended for a specified time period under specified operating conditions. Product reliability assessment is nearly always based on accelerated life test statistical modeling and projections. For LED lighting systems, both lumen depreciation and failures of other components contribute to overall reliability

    In the context of field operation, robustness is an unquantified indication of the ability of a product or system to operate as intended in the specified environment by confirming that design and production processes yield products that can withstand higher levels of stress than would be expected in normal operation. The electronics industry has for decades employed robustness testing protocols as part of their verification programs. The concept has only recently been embraced by the greater LED lighting community, as the realization has taken hold that LED-based lighting products are not much different from other types of electronics, except, of course, that they produce light.

    Robustness testing typically involves subjecting production samples to a variety of overstress conditions, making it more part of an overall QA program as opposed to reliability testing that uses design prototypes. And unlike reliability testing where the goal is to test to failure to learn about failure modes, the expectation for robustness tests is that all products will operate correctly at the conclusion of the test.

    Robustness tests for LED lighting are similar to tests for other types of electronic equipment published by JEDEC, IEC, and other organizations, but tailored to the special characteristics of LED products.

    Reply
  10. Tomi Engdahl says:

    How long do LEDs really last?
    http://www.edn.com/electronics-blogs/led-zone/4441442/How-long-do-LEDs-really-last-

    I was contemplating my own mortality recently, when I realized 2015 passed by in a blur. Ruminating about the loss of yet one more year, I looked at my LED-laden lamp and thought, “Sure, you might last 50,000 hours, while my expiration date is virtually unknown.” But, was this true?

    Happy to take the thought process from my own shelf life to that of an LED, I began to wonder if that 50,000, 35,000, or 25,000 hours of use from an LED could possibly be accurate. For one thing, I don’t mark down the date of purchase for my LEDs. Do you?

    The article discussed tests on five samples of 46 types of bulbs by European partners and consumer watchdogs. The test involved turning bulbs on for 165 minutes and off for 15 minutes until failure. The results of the test:

    Five types stopped working before 6,000 hours
    Five with claims of at least 25,000 hours stopped before 10,000 hours
    66 out of 230 samples failed before 10,000 hours even though claims were for at least 15,000 hours of use

    Not a fan of the Daily Mail? What might you believe? The U.S. Department of Energy’s website discusses tests for a variety of bulb types. For instance, it states that, “CFLs are tested according to LM-65, published by the Illuminating Engineering Society of North America (IESNA). A statistically valid sample of lamps is tested at an ambient temperature of 25° C using an operating cycle of 3 hours on and 20 minutes off. The point at which half the lamps in the sample have failed is the rated average life for that lamp. For 10,000 hour lamps, this process takes about 15 months.”

    In that vein, how long do you think a bulb claiming 50,000 hours would need to be tested? Try 5.7 years. What it comes down to is that there seem to be no real sure-fire ways to test the long-term performance/viability of the LED.

    Those cost and performance figures seem to be drawn out of the thinnest of air.

    Reply

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