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LED Christmas lights

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    LED Christmas lights

    Because of a peculiar visual defect, I can detect LED Christmas lights flickering immediately and from a considerable distance. Lately, I've even noticed that the LED tail lamps on some vehicles have a flicker to them.

    In both cases, the flicker rate is about 60Hz and to my eye is extremely irritating.

    Last January, I picked up a few cheap strings of LED Christmas lights and just got them out today. Sure enough, the manufacturers use the individual LEDs in series as a half-wave configuration, so that the flicker rate is indeed 60Hz.

    I've made an adapter where the AC line is run through a bridge rectifier and thus provides a full-wave 120Hz-ripple supply. The LEDs are considerably brighter (of course), and the discernible flicker is gone. I'm using a 10A bridge, so even if a conventional string of incandescent lights is plugged in, it won't overtax the circuit.

    But this got me thinking about the wider ramifications of the current scheme. You'd think that the power companies would have an issue with a half-wave setup, loading the line only on alternate half-cycles. Yet I've heard not a peep from any industry spokesperson.

    Anyone know why?
    Reach me: vcfblackhole _at_ protonmail dot com.

    #2
    I'd guess that the total number of LEDs in use right now is such a tiny power draw that it would hardly be noticed. I could be wrong, but I am pretty sure the new LED lamps for standard sockets do things differently to avoid flicker. I have one that is dimmable, which clearly requires some more circuitry (maybe PWM?).

    Comment


      #3
      I refuse to buy the led xmas lights. But I have friends who went out and replaced every string with led's... *sigh*

      I thought I was crazy about the flicker. thanks for that. And I must admit thats a pretty crafty way to get rid of the flicker with that bridge...
      It is a mistake to think you can solve any major problems just with potatoes.

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        #4
        Originally posted by luckybob View Post
        I thought I was crazy about the flicker. thanks for that.
        Me too. Everyone was telling me I was nuts, that there was no flicker in the LED lights.

        Comment


          #5
          Good catch Chuck, and an elegant solution.

          This half wave load is indeed a question. I would think that mark66j is right, in that there is not a big load from christmas lights. However, could it also be that the polarity cancels out with a large number of users?

          PS: This is getting out of my depth here, but the roughly 50% power factor of CFLs seems like a related issue, and we're not seeing complaints about that either. I think it's time for another conspiracy theory.
          WANTED: Cardinal 2450MNP modem.

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            #6
            I hate LED Christmas light because of the flickering and because the blue and green bulbs are way too bright compared to the other colors. Battery-operated LED lights eliminate the flickering, but still have the odd color balance. However, as my friend Chris discovered, simply adding a resistor in series with the lights to drop the voltage slightly, dims down the blue and green LEDs but doesn't affect the output of the other colors, providing a much more pleasing color balance:

            LED Christmas lights - tweaking
            http://www.youtube.com/watch?v=B_jMHRLnOco

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              #7
              I have a string of LED lights going around my room.
              The lights are similar to that of the older incandescent type. There's a white LED in a colored glass tube so I haven't seen the green/blue overbrightness yet but the flicker is quite noticeable.

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                #8
                I would like to upload a copy of the schematic, but again, it is copyrighted. Does anyone know if it's ok to upload a scan of it?

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                  #9
                  I never liked LED Christmas lights. Their colors seem so drab and cold compared to the bright, cheerful character of the traditional incandescent miniature lamps.
                  Latest Acquisitions: ADDS Envoy, Sun 3/50, Teletype BLIT, DECMate II
                  Still Wanted: Ithaca Intersystems DPS-1, SSB Chieftain, Altos 2086, TRS-80 Model 16, Victory FACTOR
                  Always looking for: AT&T 3B2's and UnixPC/3B1's.
                  http://www.securix.net/retrotekvintagecomputers

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                    #10
                    They put those LED fairy lights around the headlights on cars in Europe now. Especially german cars and SUVs just to give them even more of an agressive look when they're right in your rear view mirror.

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                      #11
                      From monitoring the quality of our power up here with a storage scope, I get the impression the power company has it's hand full just keeping the grid up, let alone worry about the voltage or quality.
                      Besides, wouldn't some of that uneven loading effect smooth out after miles of inductance, conductor/conductor capacitance, and lastly all the transformers it propagates through ?
                      patscc

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                        #12
                        Chuck(G), do older-style VFD's bother you as well ?
                        patscc

                        Comment


                          #13
                          Yup, but since they don't occupy my entire field of vision, I'm not bothered as much.

                          One perplexing thing is that I now see cars with rear brake lights powered by what seems to be low frequency AC PWM maybe?) --at least they have a discernible flicker. Why the designers do that, I don't know. I'm not up to snuff on modern automotive electronics.

                          It used to be that I could also pick out traffic signals that have been converted to LED, but the technology must have changed since the early days, because I no longer see the flicker.
                          Reach me: vcfblackhole _at_ protonmail dot com.

                          Comment


                            #14
                            I think they had problems with the noise, spikes, and load fluctuation in a car's 12V system, so now they use a secondary regulator/driver to drive the LED's. Makes it easier to regulate brightness, flash, etc.
                            patscc

                            Comment


                              #15
                              Aren't most lights and things at 60Hz? I thought that was why computer monitors flicker on video and fluorescent office lights have that affect. Off topic, some folks in the robotics group go after the holidays are over and pick up strands of led or regular lights for whatever% off since it's usually cheaper than buying the little leds separately.
                              Looking to acquire: IBM 5100, Altair 8800

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