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  • Author Author: Gough Lui
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Click MR16 LED Globe Failure Post-Mortem

Gough Lui

One of my regular blog readers submitted an LED globe for post-mortem analysis, having failed well before the expected lifetime. I take a look inside, determine the configuration and analyze the relatively "anonymous" product which seems to show several design shortcomings which I discuss and think might be relevant to other readers at the element14 community.

 

The article is posted at http://goughlui.com/2016/06/01/failed-click-ltmr5w3k-5w-led-mr16-replacement-globe/

 

What really gets me is that many products are still designed using multiple-parallel LEDs without any current balancing mechanisms (e.g. remember emitter feedback resistors when paralleling BJTs?) and that leads to potential for a single string to be overstressed continually, fail early, and begin the cascade of failure as other LEDs are forced to soak up current in excess of their ratings, and operate in less efficient regimes resulting in greater heat production and degradation of the semiconductor material. Of course, if you went all-series, you would have an all or nothing situation and require higher voltage driver electronics, but I personally would gravitate to this arrangement for reliability reasons, or go with multiple independent channels if reliability is demanded.

 

Any comments, or stories related to LED globes or LED light designs are very much welcome.

 

- Gough

  • in reply to shabaz

    Over the years I have become used to working under (4)  150 Watt incandescent flood lights. Yes they were hot and probably cost a couple $ a month to operate but I needed to see the cracks and problems in the circuit boards of the equipment I was trying to fix and at that time there wasn't really any other options. As the eyes have gotten older and the availability of 150 watt floods has dried up I have had to move to 120 watt halogen bulbs. I have tried some CFL floods but they are slow to come up to intensity and I just haven't been able to warm up to them ( pun intended). Here is my present bench lighting system with (4) 120 Watt halogen floods, (3) 75 watt incandescent floods and about 160 watts of overhead florescent. The bench lighting is switchable so it all isn't on at one time unless it is needed. So far the LED bulbs either look too expensive or too experimental. 's bulb autopsy hasn't made me any more inclined to try them either. Here are a couple shots of the lighting above the bench and what the bench itself looks like. 

     

        imageimage

     

    John

  • in reply to mcb1

    Exactly, we need brightness! depressing that it is the start of June and weather still isn't great.

    For a work task lamp I'm using a Sylvania RefLED Par16 5W E14 model, and overall I think I'll stick with it - 3000K, and runs cold of course.

    In the garage I've got fluorescent lighting, but also as a temporary measure LED strip-lighting near the bench and power tools, but it isn't great, barely adequate. There is also a portable fluorescent lamp there that I can move around depending on what I'm working on. I really do need to reconsider that area a lot, it wouldn't pass brightness levels for safety I bet.

  • in reply to mcb1

    We get either warm white (2700k most brands, 3000k for Philips) or daylight (6500k but only select sizes of Philips and Osram). On the whole, most people seem to prefer warm white inside, so I suspect the stockists don't stock the other lines for the most part - any other CCTs, you're going to have to go with some smart globe.

     

    While the LEDs are bright, many report that the latest high-efficiency units have a steep initial lumen depreciation, so they will be impressive when first turned on, but after the first few hundred hours, they will "do most of their degradation" and sit close to 80-90% of the initial output for the remainder until failure.

     

    - Gough

  • in reply to shabaz

    I get the feeling that without mixing LED colors*, this problem would be hard to get rid of

    All the LED lamps I saw in AUS were warm colour.

    many were of the 60 or more degrees, which makes them useless for task lighting over benches, etc.

     

    The consensus is basically it is definitely brighter

    So England is the right place to test these, NZ and AUS have sunlight ...  image

     

     

    I do have a couple of places to fit LED, but in talking to the electrical supplier there seems to be no direct replacements for my Dicrohics .... yet.

    Mark

  • in reply to shabaz

    Lots of opinions out there, and lots of different quality. The majors tend to do it okay, but the consumer level products of some brands are merely rebadged products OEMed from some company in China (e.g. Leedarson OEMs for Ikea, OSRAM (Sylvania) Lightify (Tunable White only) and Belkin WeMo for example).

     

    On the whole, I won't say I'm "in a hurry" but I've got more than a few LED globes. Almost half the house is LED globes, and soon, even more will be LED purely because I dislike some of CFL's disadvantages (mainly cycle life, warm-up time). The light quality indeed is poorer for many of the economy LEDs and they boil down to the CRI being on the high 70's to low 80's. The better ones score top out at a CRI of about 85 at the most when it comes to those which use white LEDs because of the physics of using ~460nm blue + a phosphor mix to give yellows and reds which still leaves a nice gap in the greens.

     

    An improvement in CRI seems to be from the tunable RGBW multicolour globes that use a discrete red (623nm), blue (460nm) and green (525nm) LED to create white. The downside is that these globes are mainly expensive home automation/Zigbee control units, and they're also generally lower on output because of the added complexity of three independent control channels. But in return, you get CRIs of >85 (e.g. OSRAM Lightify) and tunable colour temperature ... and while it could be even better than that, I suspect they decided to "stop short of a technical barrier" purely because a consumer is unlikely to need CRIs greater than 90-somethings.

     

    The mixing LED colours business seems a rather interesting approach, and the tunable white globes generally achieve their tunability by "fading" two channels to mix 2700k warm white LEDs with 6500k daylight LEDs to give the "complete" range. This works but of course, the CRI doesn't necessarily improve even when choosing an intermediate colour temperature.

     

    So far, I've had one early life failure in a personally purchased and deployed globe that boiled down to a driver failure (unidentified due to the physical construction being impossible to take apart), but the remainder are going on well. Dimming with these globes where they are supported requires trailing edge dimmers, and many existing dimmers are leading edge and won't function correctly or will cause premature failure as well. Even a universal dimmer is no guarantee - I have one on the test bench at the moment which has caused me no end to frustration because it has a 10VA load minimum and even a 15W LED globe won't allow it to run stably.

     

    I suppose, environmentally, the lower energy consumption and lack of mercury gets my tick as well.

     

    - Gough