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Lighting: Calculating PUR

Discussion in 'General Plant Topics' started by ILuvMyGoldBarb, Jul 1, 2007.

  1. ILuvMyGoldBarb

    ILuvMyGoldBarb Junior Poster

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    Can someone give me the formula for calculating PUR? I've finally grasped the concept of PUR and PAR and their importance so I want to figure them out for my tank and see if I can improve my lighting.
    Thanks
     
  2. Tom Barr

    Tom Barr Founder
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    I just use PAR and use a PAR meter and that's the end of it for me:)

    Apogee makes a very nice PAR meter that's water proof etc to 6-8ft etc.
    I have one and a LICOR.

    Regards,
    Tom Barr
     
  3. ILuvMyGoldBarb

    ILuvMyGoldBarb Junior Poster

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    So is there a low tech way to calculate PAR? I have 6700K bulbs in my 4x96w PC system but I'd like to know my PAR to see if these are really that good or not. I know they look good but I would like to get the max PUR out of my lights as possible.
     
  4. Tom Barr

    Tom Barr Founder
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    Ivo use to have qa nice run down and I think some other folks spents gobs of time and effort to get at it and use a model.

    I spent some $ and can test in real time, in specfic cases, at specific plants, at specific depths etc, with a lot less guess work, time and effort.

    That's a trade off.

    One I gave some thought too... and also given the lack of light measurement in this hobby, a painfully poor black hole, decided to do something about it.

    I see some carry on about testing and measurements of little things such as NO3, Fe etc, but they do not measure light.

    Kinda of funny when they bad mouth me suggesting water changes and known volume/weights to target a NO3 levels but they do not even own a light meter:eek:

    Regards,
    Tom Barr
     
  5. detlef

    detlef Member

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    Try to contact Daniel, he might be able to give you some formula.

    www.defblog.se


    Best regards,
    Detlef
     
  6. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    I dont know if you really can 'calculate' PUR. You'd have to measure it, I mean its a property of the light and depends on its spectral distribution and intensity across a given range. To 'calculate' it youd need some accurate data if not measured by yourself, from someone else or the company, and either a whole lot of math by hand or a program to interpolate the data.

    As I understand it, LUX is weighted towards human sight, PAR is unweighted and accounts for all wavelengths 400-700nm, and PUR is weighted towards plants photosynthetic regions. The idea of PUR is good, but i've not seen any bulbs really measured with it and I have yet to hear of such a meter - is there such a thing experts?
     
  7. defdac

    defdac Lifetime Members
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    My router seems to have gone down so you can't reach my blog or my PUR-calculator.

    I calculate PUR exactly as outlined in this article:
    Aqua Botanic-light bulb comparison
    "Steps to calculate tabulated quantities"

    It uses a photosynthetic action spectrum, which is an average of how most plants use the radiation. Crazy Loaches is right that it thus can't be calculated *exactly* for one single plant - but it will be very near.
     
  8. defdac

    defdac Lifetime Members
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    Take a PAR-meter and put a filter on it that filters the light exactly like a photosynthetic action spectrum and you will get the PUR-value.

    Can be done either optically or digitally.
     
  9. VaughnH

    VaughnH Lifetime Charter Member
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    A lot of things that can be done are not of great value to actually do. Plants can adapt well to a wide range of light intensities and light spectra. So, there is little to be gained by pursuing an accurate measure of just the light that is most effective for plants. On the other hand, if you enjoy the science involved, and that is part of the pleasure this hobby provides to you, then there is no reason not to seek such light measurements. This is a hobby, so enjoyment is the goal.
     
  10. defdac

    defdac Lifetime Members
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    Would you in the same way say that plants have adapted to a wide range of nutrient levels so there i little to be gained by pursuing an accurate measure of just the nutrients/levels that is most effective for plants?

    If not, why is that?
     
  11. defdac

    defdac Lifetime Members
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    Or VaughnH, I really don't want to know your answer anyway since it's not important for me growing my plants ;)
     
  12. VaughnH

    VaughnH Lifetime Charter Member
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    You have described exactly the theory behind the EI method of fertilizing. Like light, nutrient concentrations are not critical for growing plants. Having an adequate concentration is all that is needed, so long as you don't go way overboard, and weekly water changes take care of that problem.

    As I said before, those who enjoy applying a more rigorous scientific study to growing plants should continue to do so. It is a hobby, so whatever aspects of that hobby make it more enjoyable are the aspects you should do more of. But, those who just want to be able to grow healthy aquatic plants and have an attractive aquarium, should not be misled into believing that scientific accuracy is a prerequisite to accomplishing that. (That's why we keep Tom around!)
     
  13. defdac

    defdac Lifetime Members
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    True, its just that I without the knowledge of PAR/PUR-calculations wouldn't have figured out that the wpg-rule can be a bit misleading sometimes and also never gotten any feel for how little PAR/PUR we actually got in most setups. It is quite enlightening to dwelve into the details, and also fun.

    But I agree, it's not needed in most cases to run a nice planted tank =)
     
  14. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    Ah yes, that should work! But does such an optical filter exist that would be readily available to hobbyist? If your doing the conversion digitally then you need a meter that will take an entire spectral analysis - something thats probably out of reach for 99.99% of hobbyists. I've linked that aqua botanic light comparison many times, its a great source of info. But I question some of the data... like "I used only spectral curves and bulb data I was able to get from the web"... hmmm. And the bulb list there is a bit old.

    Overall though, the main difference I see between PAR and PUR is that light in the green range isnt usefull much to plants so it can inflate PAR figures. But green still is usefull, it makes plants really 'glow'.
     
  15. Professor Myers

    Professor Myers Guru Class Expert

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    Amen !!! I've tested systems with clinical precision for years. All things considered I have enjoyed greater success with Basic EI ! :)

    Don't know why exactly, and honestly Don't Care ! If it ain't broke...Don't Fix It !!!

    Common sense ain't so very common. ;)
     
  16. ILuvMyGoldBarb

    ILuvMyGoldBarb Junior Poster

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    My main reason for being interested in this is due to the fact that I want to make sure I don't have somehting like I saw in a store. A 6700K bulb that had a huge spike in the Yellow/Green spectrum and hardly anything in the red and very little in the blue. Just wanting to get the best possible bulbs for my tank.
     
  17. Left C

    Left C Lifetime Members
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    Does your fixture use straight pin bulbs? Would you want to try the GE 9325K 55w straight pin PCs? You could use two of these with two of your 6700K bulbs.

    Here's two places that sell them:
    55 Watt 20.7" 4 Pin Biax - Aquarium Fresh & Saltwater Phosphor: Light Bulbs Etc, Inc.
    55W AQUARIUM BULB $14.19 F55BX/AR/FS GE 55 WATT 4800 LUMEN 9325K 67 CRI 20.70 INCH FRESH SALT WATER Atlanta Light Bulbs Inc.
     
  18. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    That would describe most bulbs in the 6500/6700K range IME, I'm sure the Philips Daylight Delux bulbs I am using are the same way, as you can actually see some green tint to them barely, but many use them with success. Bulbs without very much green usually appear somewhere between pinkish and purple to your eyes. Like one bulb I tried, the Lightning Rod Aqua-Flora Plus, very little green according to thier little spectrum chart and the bulb is purplish.
     
  19. ILuvMyGoldBarb

    ILuvMyGoldBarb Junior Poster

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    Thanks for the links, but my fixture fails on both counts. :) It's a 4x96w SQ pin fixture.
     
  20. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    Your options are much less with the 96 watt'ers, as I'm sure you already know.
     
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