Light Meters

Discussion in 'Lighting' started by dsomers, May 20, 2015.

  1. #1 dsomers, May 20, 2015
    I want to get a light meter and am trying to figure out the different kinds.  So far my understanding is that cheaper, regular light meters only measure visible light and that to get one that measures PAR you have to spend much more money.  The key question then is how well a regular, visible light meter estimates PAR.  Is a regular meter good enough?  Does it depend on the spectrum of the grow light you're measuring?  Or do you really need the expensive PAR meter to get a useful reading?  Thanks

     
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  2. #2 REALSTYLES, May 23, 2015
    What I was told by some of the great led gurus is you can use a lux meter and convert lux into Umols or miromols that = PAR. It's lux / either 66 warm led or 69 cool led to get the Umols.
     
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  3. #3 Icemud, May 24, 2015
    Your best bet would be to spend the money on either an apogee mq200 or a li-cor which are pretty much the standard. The apogee retails around $360 but I found mine on ebay for around $240. The Li-Cor is much more accurate than the apogee but also is around $1000.
     
    A lux meter wont really be sufficient, even though you can convert Lux to par, its kind of pain because when converting lux to par, you have to take into consideration the spectrum, (amount of red, green, blue) because this will change your calculations. For instance if you had a MH and a HPS with both the same lux output, they would convert to PAR (umol/m2/s-1) differently due to the different spectral output.
     
    So with that being said, a PAR meter will be your best bet, also known as a quantum meter.... that is unless you have more money to spend and then I would recommend a spectroradiometer, but they start around $3500
     
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  4. #4 REALSTYLES, May 27, 2015
    Last edited by a moderator: May 27, 2015
    You are almost correct. The Apogee will not give the right PAR readings on the white cob leds due to the far red and far blue they give off. I think has a conversion on their site. The sensor that works correctly costs $5000 for the cobs.
     
  5. #5 Icemud, May 27, 2015
    Here are the numbers for the apogee error correction.. still will do an ok job for judging light height and coverage area's. For accurate readings though, spectroradiometer all the way.
    Blue(448nm)‐10.7
    Green(524nm)5.8
    Red(635nm)4.7
    Red,Blue2.7
    Red,Green,Blue3.5
     
    When I spoke with Apogee's engineer for a good hour, he told me when measuring multi wavelength diodes in LED arrays like grow lights, the apogee meter will read less than a 5% error margin, which for most application is pretty good.
     
    ***the engineer also told me the sun system quantum meters are exactly the same as the MQ200, except for the label. All internals are identical as they come off  the same line. :)
     

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