PWM LED Dimming

Discussion in 'Lighting' started by moz, 23 Sep 2008.

  1. moz

    moz

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    I’ve been doing some research on LED lighting using high power (>1W) LED. It seem the preferred method for “dimming” is through Pulse width modulation (PWM) if I understand it correctly the LEDs are not being dimmed but rather being turned on or off at a rate that makes them appear to be dimmer. I’m assuming that these frequencies are designed for humans, does anybody know of where I can get more information on the affects of PWM on reef systems?
     
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  3. lIghty

    lIghty

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    Hi Moz

    I've done some homework on this too, you are correct, PWM it exactly that, the time period that the light is on verse off is called the duty cycle, the frequency at which this happens is usually about 100hz to 1khz, this would not make any difference if it was for humans of reef (to my knowledge), but rather on the specs of LED used.

    I actually bought a oscilloscope 2 weeks ago to start doing some prototypes....

    But to take one step back, What are you wanting to do with the LED lighting?
     
  4. moz

    moz Thread Starter

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    At the moment, I'm just planning on experimenting (half tank on LED's other half on MH), and then hopefully a full lighting system similar to the Solaris for my planned future setup.
     
  5. lIghty

    lIghty

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    what i've found so far is that the high power leds are generally expensive, and to get the correct colour light you have to supplement with other leds or use a the method of using and controlling bi or tri-colour leds. how deep is the tank you wanna test it on.
     
  6. moz

    moz Thread Starter

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    The tank is 600mm deep, I have been thinking of a 60/40 white/blue mix. Below is the light output for the 3W leds[​IMG]
    [​IMG]
     
  7. lIghty

    lIghty

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    Think 60/40 split may be a bit too much on the blue side, If you look at the "white" led curve, its main peak is at 460-470nm, which will give a rather blue hue. What make/model LED is this, if you could provide WWW page I would appreciate it.

    Do you have any experience in electronics, and how keen are you to do some serious development?
    </IMG>
     
  8. moz

    moz Thread Starter

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    My electronics experience is very limited (1st year physics). So I'm not the right person to do any serious development, luckily allot of the components (LED's, drivers, power supply's) for led lighting is readily available.

    The LED's I plan on using are;
    ProLight Opto
     
  9. lIghty

    lIghty

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    Just check my records, gonna work out extremely expensive to build, see below

    *please note, used a Compact Florescent Lamp in comparison, T5 is even better.

    1w LED - R29 - 80 lm - 2.75 lm/R - 80 lm/W
    3w LED - R45 - 170 lm - 3.77 lm/R - 56 lm/W

    14w CFL - R15 - 800 lm - 53.33 lm/R - 57 lm/W

    As you can see, lm/R, the CFL works out much cheaper & lm/W the 1W LED is best.

    so what does this mean? yes the 1W LED has higher lumen output per watt electricity, used but is 20 times more expensive than the CFL but uses about 28% less electricity. Is it really worth it?
     
  10. Warr7207

    Warr7207

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    One other factor, how long will it last and keep the correct light intensity and spectrum ?
     
  11. lIghty

    lIghty

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    They would last for years, and intensity and spectrum will only vary little over this time.
     
  12. Warr7207

    Warr7207

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    Then the calculation should be done with this factor included. The initial outlay is going be high, but the saving on power usage and globe replacement may work out cheaper.

    Also less cooling power needed ;)
     
  13. lIghty

    lIghty

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    Yes you would save money on electricity and replacement bulbs over the years, but you would probably make more if you invested the difference in the initial purchase in a investment with Liberty Life or some one:whistling:, with regards to heat, this can be tricky, some of the High Power LEDs produce a little under what a T5 would make, so yes, they not as hot but nothing that will make a really big difference IMHO.
    </IMG>
     
  14. Warr7207

    Warr7207

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    Cool, if we didn't spend the bucks on these tanks we would all be better off, but I understand what you saying.

    Also as the tech is developed the pricing will reduce. I saw T5's LED globes costing around R400-R600, so it should not be long before LED is a viable option ;)
     
  15. lIghty

    lIghty

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    I say give it 5 years and we'll all be using LED, prices just have to come down 1st.
     
  16. moz

    moz Thread Starter

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    Which LED are you using for comparison, the 3W I'm thinking of using
    3w LED ~ R25 - 110 lm
    1w LED ~ R20 - 35 lm
    Also LEDs generally have Photosynthetically Active Radiation (PAR) and Photosynthetic Photon Flux (PPF) levels comparable (sometimes higher) to MH's while CFL don't come close.
     
  17. lIghty

    lIghty

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    Thats true, we have to take that into account, unfortunately it doesn't state it on the Spec sheets.

    http://www.wahwang.com/pdf/WW-E101WL1-W4.pdf - 1W LED

    http://www.wahwang.com/pdf/WW-E203WH1-W1.pdf - 3W LED

    Why do you find the PAR rating, build one and test?
     
  18. moz

    moz Thread Starter

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    Don't know what the PAR rating is, but on all the reviews/test of commercial reef LED's the PAR have been better than MH's. The Solaris used the Luxeon K2 (R50-R65) which if I have the correct model are 100 lm.

    At the moment I'm just going to build a 5x5 unit to test.
     
  19. lIghty

    lIghty

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    Their new unit that are made in the states use 30 Luxeon Rebel opposed to the old 25 Luxeon K2 setup.

    Correct

    Old K2 was 100lm @1000ma

    New will run at about 140lm @ 800ma if i'm correct, and will cost about R83.

    Please post some pics on this thread, would love to see it in action!
     
  20. Mekaeel

    Mekaeel Moderator MASA Contributor

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    You fellas who are planning on designing these units. How about this idea:
    1 row blue
    1 row red
    2 rows white.........
    Keep it in that sequence. It will be like the way that KZ does recommends using the Fiji Purple T5's.
    Just a thought :)
     
  21. Warr7207

    Warr7207

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    What are your thoughts on this ? I am getting a sample this weekend to try out.



    [​IMG]

    CONTROL FEATURES


    5-channel DMX-512 LED washlight
    Blackout/static/dimmer/strobe
    Static colors and RGB color mixing with or without DMX controller ADDITIONAL FEATURES

    Additional power output for daisy chaining units together (max 50 units)
    Built-in automated programs via master/slave
    Low-power consumption

    SPECIFICATIONS

    Beam angle: 16°
    Footcandles: 39
    Lux: 411
    Light Source: 86 (44 red, 21 green, 21 blue) LEDs 100,000hrs
    Current draw: (peak 24W @ 120V) (inrush 0W@ 120V)
    Power: Switchable 110V/230V 50/60Hz
    Weight: 1kg
    Size: 121mm x 168mm x 102mm 2-year limited warranty
     
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