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When using LEDs, what constitutes "high light" level?

Discussion in 'Lighting' started by evangemeren, Sep 4, 2017.

  1. evangemeren

    evangemeren Junior Poster

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    Newbie question here ... (NOTE: site admins - sorry for the double-post ... I also posted this in the "new to plants" thread ... hope that's OK ... this is my first post)

    I'm following Tom's guidelines and doing my homework, but before choosing a method I want to follow it is clear I need to understand how much lighting I am really working with. There is a TON of data when dealing with fluorescent fixtures or metal halides, but I'm using LEDs which clearly seem to be different.

    I purchased a 24" Current USA Satellite Plus PRO, which is supposed to be good for "high light level plants" (according to the manufacturer, anyway). Since I don't have a PAR meter, I am going by the manufacturer's specs, which claim the unit puts out 30 Watts and 2,000 Lumens, and has a PAR value of 100+ at 12" water depth.

    I have a 40 gal tank that is quite deep (15" from surface to top of substrate) and the light is 7" from the surface.

    While I'm still trying to nail down which method I will follow, I am currently using CO2 injection, and my drop checker shows a consistent 30 ppm. I've also cross-checked this based on my alkalinity (6 degrees) and pH (6.8).

    Questions:

    1) I see lots of recommendations on what PAR level I need to produce, but I am confused as to where to measure that. It makes sense that one would measure this at the substrate for low-lying foreground plants, but I also have things like Wisteria and Amazon Swords which grow quite tall - for these plants wouldn't it be more relevant to measure the PAR level at the depth where the foliage occurs?

    2) Is there a simple guide that lists the required PAR levels for each species of plant? I see that this is listed for the few species that are in the "Plant Database" on this site, but only shows a few entries. Is there another resource I should look to?

    3) how reliable are the manufacturer's stated performance figures for PAR levels? Can I use the data provided as-read, or is there another resource I can use that provides PAR levels based on independent testing? I found a few videos of this on YouTube, but not sure how reliable the sources are.

    Any thoughts would be appreciated.
     
    DutchMuch likes this.
  2. bshenanagins

    bshenanagins Junior Poster

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    Manufacturer numbers are typically based on open air calculations, meaning there will be a difference in PAR when water is added. However I think your good at the moment with the height level so just make are that the co2 stays stable and plenty of macros/micros and you should be okay. You can raise or lower the lights based on growth
     
  3. evangemeren

    evangemeren Junior Poster

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    Update ... I may be a wee bit OCD, so I went out and purchased the APEX PMK (PAR monitoring kit) and connected it to my APEX controller.

    In case you were curious, the unit says I am getting a PAR reading of 20 in the center of the tank (i.e. immediately below the light fixture) at the level of the substrate, and 17 in either of the 4 corners of the tank (i.e. off the axis of the light fixture).

    Hmmm ... a lot less than the "100+" quoted by the manufacturer ... but then again, perhaps this sensor isn't 100% accurate either.

    Regardless ... that would suggest that my tank falls into the category of "low light", doesn't it?

    Again, but isn't it equally important to consider the PAR level at shallower depths where some of the background foliage grows?
     
  4. Phishless

    Phishless Lifetime Member
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    I measure PAR @ substrate level.
    Granted it is a lot higher near the surface.

    Light is very deceptive when we are the judge(opinions you know).

    Until I purchased a PAR meter I was way off just estimating.
     
  5. tiger15

    tiger15 Member

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    Have you tried the Rotala light calculator.

    http://www.rotalabutterfly.com/light-calculator.php

    I plugged in your data, selected LED Cree, and got 20 PAR at the substrate level in the center, matching your measurement.
    Changing the scenario, the calculated PAR is 69 at 12" depth, so it is not too far off from manufacture's info.







    upload_2017-9-10_9-15-10.png
     
    Jason King likes this.
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