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Thema: why GHL take 200Hz PWM on LX7206

  1. #1
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    Frage why GHL take 200Hz PWM on LX7206

    200Hz PWM is too low frequency, you can easily capture by your phone when taking slow motion or video.

    I can understand the huge power dissipation of 72 diodes. But I think the big heat sinker + 3 fans, which should be enough for maximum power. In case overheating, you have complete safe protection of LED diodes.

    meanwhile, I am questioning PWM. No sure the negative impact to fish or corals. Because nature lights, has no such PWM regulation.
    If compare with US competitors, none of them take such low PWM frequency. All of them are using much higher frequency, e.g. 100KHz. It will be no impact to the photograph video taking.

    Can you consider to improve this in next firmware upgrade?

    PS, I know you provide the photo mode in GCC. But can you introduce on touch panel or GHL connect for quick access.
    Thanks.

  2. #2
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    the real filed test is only 150Hz. Still wondering why GHL engineer take so low value, which already can be captured by smart phone camera.
    If purely for energy saving, I disagree it. Because you can keep the PWM, but increase the frequency, e.g. 1KHz? The only possible reason is the limitation of MCU computing power, difficult to manage 12 driving channel in parallel.

    Any one can clarify here?
    Thanks.

  3. #3
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    13.08.2010
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    200HZ for corals and fish a problem??? 50-60HZ HQI /T5/T8 or other no problem???
    What do fish be interested what you see with your smartphone?

    For a detailed opinion you will probably have to wait for some information from GHL.

    regards pit

  4. #4
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    for long term, I think it matters.
    The artificial lights always try to mimic the natural sun light. I think these ocean creature will never experience this pwm lighting in their life, except in our aquarium tank.

    Meanwhile, taking the comparison from GHL major U.S. competitors, most of them use much much high PWM frequency to reduce the light flicking.
    So I would like to understand why GHL take this choice.

    Anyway, I love my 4 GHL LX7206, almost perfect LED lights on the market. If GHL can fix this drawback further, it will become truly unbeatable.

  5. #5
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    The sunlight should be around 600THz, which means
    600,000,000,000,000 kHz. And you think you can get near the sunlight with 100KHz or more.
    For me, it's pure marketing, what brings more problems than advantages. Which of course doesn't mean that GHL can't optimize anything. But this is not done with a firmware update.

    regards Pit

  6. #6
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    Thanks for your reply.

    GHL used a very powerful microcontroller in LX7206, CYPRESS, MB9B500B series, which is 32-bit ARM cortext M3 core, 80MHz operation frequency.
    I guess GHL use GPIO to toggling the PWM signal for each channel. So by increasing this PWM frequency, it should be feasible to realize by upgrading the firmware.

    Hoping this post can be passed to GHL engineer and may feedback on this.
    Thanks.

  7. #7
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    Hello,

    thanks for your input. I will forward your feature request to the responsible engineers referring to this thread, when they returned from the trip to ReefAPalooza.
    No support or warranty issues over PM! Please send PMs to the moderators only if you have general problems with using the forum! Thanks for helping us to keep the support efficient.
    Kein Support oder Reklamationsabwicklung über PM! Bitte senden Sie an die Moderatoren nur PMs bei allgemeinen Problemen mit der Verwendung des Forums! Danke dass Sie uns dabei helfen, den Support effektiv zu gestalten.

  8. #8
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    Of course we could change the PWM frequency. We do this already when the LX7 is in photo mode.

    But we don't use a higher frequency as standard on purpose due to energy efficiacy. The higher the frequency the higher the loss. And there is also another reason, see below.

    Also the LX6 worked on this frequency, so we had it now for about 7 years. Not ever a problem reported. Not sure where your concrete problem lies.
    As already mentioned, MH or T8/T12 had 50/60Hz.

    However, I already thought about changing the frequency in a coming firmware version a bit, as a compromise between efficiacy and the visibility for cameras.

    To
    If compare with US competitors, none of them take such low PWM frequency. All of them are using much higher frequency, e.g. 100KHz.
    This is wrong. You would NEVER dim a LED with a PWM frequency of 100kHz.
    What you mean is the frequency of the switching current controller. LED current controllers have a switching frequency of 100kHz ... 1MHz.
    But the dimming PWM must be this frequency divided by 1000 ... 3000, depending on the dimming steps you want to have.

    Since the LX7 has 3000 dimming steps we talk about max. PWM of 300Hz.

    You see, it is not only the efficiacy, it is also the dimming resolution which depends on the dimming PWM.

    -> as said, I planned to have a closer look into this with future updates
    No support or warranty issues over PM! Please send PMs to the moderators only if you have general problems with using the forum! Thanks for helping us to keep the support efficient.
    Kein Support oder Reklamationsabwicklung über PM! Bitte senden Sie an die Moderatoren nur PMs bei allgemeinen Problemen mit der Verwendung des Forums! Danke dass Sie uns dabei helfen, den Support effektiv zu gestalten.

  9. #9
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    Hi, Matthias. Really appreciate for your feedback and comments.

    I am fully understand the intention to use PWM method to improve the energy efficiency. But we still can find some sweet point(higher freq), at least to above 120fps, so that the pwm switching will not captured by camera. Maybe you can even skip this photo mode.

    Regarding to the photo mode, I noticed significant color shifting compare with high eff. / high power mode. I guess the spectrum in light composer is characterized with pwm mode instead of photo mode, right? So I would still stick with pwm mode for spectrum tuning.

    One major drawback of PWM is that it dramatically reduce the numbers of photons which will be emitted to coral. The coral is fed on it. Currently more and more focus on DLI, which is counting the overall energy which distribute to coral daily. High intensity+shorter time or middle intensity+ longer time. Because investigation shows it greatly impact on growth quantity and quality.

    Maybe I can give you some hint , which can introduce into the next firmware upgrade. Axxx use >500KHz buck LED driver IC, Exxxxxx, use >200KHz switching freq.

    For dimming step, I don't think 3000 step make more sense to current above 100mA(for example), eyes can not tell the difference. But for moon light or low intensity(e.g.<10%), it really needs it. So why not set some boundary condition, if above certain percentage, take higher PWM freq and if below take low PWM freq to achieve best dimming effect. One of your competitor already did like this way.

    One more thing, did you already consider to implement power shifting for LX7206 9 channels?

    Sorry, talking too much. But I am truly love LX7206, I want it to be THE perfect one.

  10. #10
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    Hi, Matthias. Do you have some working email? I would like to discuss with you about one advanced light control method, which could be a Unique Selling Point for LX7206.

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