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LED lamps vs fluorescent lamps?

Discussion in 'General Electronics Chat' started by Flyback, Sep 8, 2013.

  1. Flyback

    Flyback Well-Known Member

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    -this is interesting.
    -maybe the people who payed for it were prepared for this kind of attrition rate(?)
    -I originally though that the leds may be specially made to fail short, so as to keep current flow to other leds in the lite of failures.....but alas no, AudioGuru says they are randomly spread.

    196 leds cheaply paralleled......requires voltage of ~124V and no heatsink, wheras a single 196 led string needs ~490V and no heatsink.

    49 124mA rated leds in series would also require ~124V, but likely needs a heatsink of alu behind the led pcb.....difficult to mount a alu piece behind the led pcb as the 'stubs' of the PTH LED legs stick through.
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    ........ until 1 of the 4 paralleled LEDs fails. If it fails open circuit then the other 3 pass 41mA each, until another one fails......
     
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  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I agree.
    Make a video of the resulting smoke.
     
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  4. dave

    Dave New Member

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  5. Flyback

    Flyback Well-Known Member

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    My thoughts exactly, but this is Made in China….all companies in China are owned by the State, and so the State can arrange for each company to benefit from high volume component production…
    The Chinese state will commandere a Chinese LED foundry for a day or two, and order them to make 40mA rated LEDs in the millions, and to optimise the silicon process toward equalised Vf’s amongst the LEDs…(rather than optimising for chromaticity, etc etc), and also , they will get the foundry to add resistance into the bulk semiconductor of the LEDs, so that these leds can be paralleled.
    Because the Chinese state owns all electronics companies, it can do this in high volume, and make certain companies that it owns make products with the customised leds that it has just produced in the millions.
    The biggest laugh is when you see Western companies trying to copy this parallel operation, but stupidly use standard LEDs from a certain Vf batch, not knowing that even equal Vf groups of standard leds vary by up to 250mV in Vf….the Chinese ones, (from their special process), are virtually equal in Vf).
    How do I know that the Chinese add resistance in to the bulk semiconductor of some of their leds so that they can be paralleled?…..well, we took apart a Chinese “72 led lamp”, and found all 72 white leds in parallel, (actually three groups of 24 leds in parallel, each group of 24 having a 10R resistor upstream of it.).
    Each white led carried just 8mA….but had a Vf of 2.96V. –That proves that the Chinese added bulk semiconductor resistance to each led’s semiconductor material…because theres no way that you’d otherwise get 2.96V across even a white led that’s carrying just a puny 8mA.
    Every now and again the process goes awry , and the Chinese product fails in the field, -but then all the Chinese company does is “close itself down”,and start up again under a different name, and pull in some more Western customers under the different name.
    This whole thing of course, takes place with Western “middle men” overseeing it all and acting as the go-between to the western markets, and screwing their own Western companys in the process.
    The East has seen that Western capitalism works to a point….but can be turned on itself, to their own advantage..The capitalistic structure makes individual's and companies operate only with self interest..so the Chinese give the Western "middle men" an "£interest", and then these western middle men go forth and help the Chinese to put their own western countrymen and companies out of business...the biggest "sucker " for this is UK.
     
    Last edited: Sep 15, 2013
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,

    Wow that's weird too. I would think that the driver was not designed properly. The lights that i have seen with LED's that failed all have overdriven the LED's. The rest still work well.

    It is a very well known fact that the life of the LED decreases dramatically with an increase in current, and the life is extended many times over by underdriving. For a traffic light, they should be under driving it and making sure that temperature does not cause an increase in current too. They should also have a shade protecting them from direct sunlight as outdoor products can suffer tremendous wear just from the sunlight alone.
     
  7. Flyback

    Flyback Well-Known Member

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    I think if we were going to do a 15W led traffic light, with obviously western leds, then we'd just have to use nine SMT 700mA Red LEDs in series and use thermal vias to the bottom copper, then a aluminium plate behind it to act as a heatsink.

    If we needed to use 196 leds to get the heat spreading effect and thus loose the heatsink, then I think we'd do two strings of 98 leds-in-series, and have a separate (hysteretic or constant off time type) switch mode regulator for each string, each regulator bucking down from a 300VDC offline flyback output.

    Doing one series string of 196 leds would maybe be unwise as if one led got a dry joint, then none would shine at all.
     
  8. alec_t

    alec_t Well-Known Member Most Helpful Member

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    They may be pseudo-randomly distributed so that failed LEDs in a series or parallel group are less noticeable than if they were in line.
     
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  9. Flyback

    Flyback Well-Known Member

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    yes thats true, though with paralleled leds, you would hope that they placed the 4-in-parallel led groups together, so as to get better thermal coupling....though to be honest , I doubt the junctions will be that well thermally coupled even if situated together.
     
  10. Mike odom

    Mike odom Active Member

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    The prevalence of what is shows you what is more cost effective, not cheaper or more efficient. Fluorescent tubes have about a 50 year jump on LEDs, so no matter the increased efficiency of the LEDs, the fluorescents are going to be around for a while longer. Once the research is paid for by the LED customers, then the prices will come down. It doesn't matter how many LEDs are used in computers/tvs/etc, LED lighting is a whole new ball game and has its own development/price curve to deal with. Just the fact that developers are marketing LED lights (mains) even at higher prices shows you there is a need and an advantage for having them over fluorescent tubes. With increased use, both quantitative and over time, the LEDs will reduce in price, as R&D is paid off and manufacturing processes are vamped up. There is also a kick up in price due to popularity causing a shortage initially.

    Also the fact that most street lights, traffic lights, and cars/trucks have replaced the incandescent bulb, even though this efficiency is not an issue of this thread, shows that LEDs are more efficient in these uses as well. Cars/Trucks have more room and less power issues, so these were a natural place to start. LED lighting for mains probably spun off the need to replace traffic lights with LEDs. Even at a higher initial cost, these are more cost effective as they run cheaper (lower out of pocket long term) and last longer (less replacement cost). Most designs I have seen use both a parallel and series scheme. Like a string of christmas lights, you don't want to lose the whole bulb if one opens.
     
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  11. Mike odom

    Mike odom Active Member

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    P.S. the blue LEDs are really cool... I've waited 20 years for this!!!!!
     
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