Light meters--what rating do I need

Harry Gypsna · Oct 7, 2011

Hi there...just a quick Q about light meters.
I've been looking, and they come in differing ranges of how much light they measure to. 20 000 Lux, 50 000 Lux and then 200 000 Lux 400 000 Lux and 600 000 Lux..
Obviously the higher rated they are-the more expensive they are-the Half a million Lux meter at Growell is 70 pounds but there are some 200 000 Lux models at maplin for 30.
My question really is, will a 200 000 Lux model, or even lower rated models be suitable for getting vertical bare bulbs(1 or several) positioned correctly
Thanks :tiphat:

MIway · Oct 7, 2011

there really isn't much use in measuring anything higher than 20K... esp if you are at 1.5'+ away.

but if you can, a PAR meter would be 'better', which measure in mMols.

BigDawg · Oct 7, 2011

can you measure vertical bare bulbs? if so how

Harry Gypsna · Oct 7, 2011

MIway said:
there really isn't much use in measuring anything higher than 20K... esp if you are at 1.5'+ away.

but if you can, a PAR meter would be 'better', which measure in mMols.

OK, so getting a 50 thou model will be OK-good to know, as theyre a lot cheaper.
Ill have a look for the PAR meter, but I would imagine its a lot more expensive than the 15 pounds a 50 000 Lux photographers meter will be.
Many thanks :thank you:

growshopfrank · Oct 7, 2011

http://www.apogeeinstruments.com/quantum/?gclid=CPvS0Jj81qsCFY_CKgodACfuQA

spurr · Oct 7, 2011

@ Frank,

That's a very, very shitty quantum sensor. Almost as bad as the Specmeter versions. It's just as bad as lumen/lux/footcandle meters, re "spectral response" and being weighted for human sight, not plant growth. Check out the "quantum response", it's effing terrible!

I suggest people buy the Licor Li-190SA quantum sensor (~$380) and find a used Li-250A light meter or Li1000 datalogger or LI14000 datalogger. Or if you're an electrician/engineer you make your own lighter meter to 'read' and report the measurements from the Licor quantum sensor; call up Licor and ask for input, they can help. Anything short of that is a waste of time and you might as well buy a shitty Lux meter. Look at the quantum response of the Licor (below), yes, it's much more expensive but it's worth the price. I got my setup for ~$500 (via used LI-1000 datalogger) and it's worth ~$2,700!

@ Harry Gypsna

Please feel free to join my Quantum Sensor Working Group (social group) for much more info on these topics than you'll find anywhere else, including here and any other cannabis forum. I probably know more about these topics than all growers combined, with the exception of possibly KNNA.
https://www.icmag.com/ic/group.php?groupid=139

spurr · Oct 7, 2011

@ Harry Gypsna

I forgot to write that I have only read a single study on cannabis that looked at Lux effects on rate of photosynthesis (Pn). They found > 100,000 provides higher Pn than < 100,000. However, the study is pretty damn old (hence use of Lux and not properly using umol/area^2/second, i.e., quantum sensor).

Also, fwiw, the term "PAR" (Photosynthetically Active Radiation) is not what we measure with a quantum sensor. Many people misunderstand this important fact, including some manufacturers of quantum sensors (such as Specmeter)! We instead measure (count) the number of photons within PAR range (i.e., 400-700 nm, ideally 380-740 nm), aka PPFD (Photosynthetic Phone Flux Density) when we measure an area of meter^2. Otherwise we can't use the term PPFD because it's defined as a meter^2. Hence, I like to use "umol/area^2/second" instead of PPFD (i.e., umol/meter^2/second) because often we do not use a meter^2 canopy space.

Also, I would be remiss to not mention the topic of DLI (Daily Light Integral). See this thread with many of my posts for info on DLI: https://www.icmag.com/ic/showthread.php?t=209952

spurr · Oct 7, 2011

MIway said:
there really isn't much use in measuring anything higher than 20K... esp if you are at 1.5'+ away.

but if you can, a PAR meter would be 'better', which measure in mMols.

Cannabis can very well use > 20,000 Lux, I read one study that found highest Pn at 100,000 Lux vs < 100,000 Lux. If I were the OP, and I was going to get a Lux meter, I would get the 200,000 Lux model or the 500,000 Lux model.

Lumens are measured at lamp, Lux is measured at canopy. And we shouldn't use a PAR meter (e.g., "pyranometer"), but we should use a quantum sensor to quantify photon in PAR range. I realise you were referring to a quantum sensor when you wrote "PAR meter", but many people may think a quantum sensor is a PAR meter, when it is not.

growshopfrank · Oct 7, 2011

spurr said:
@ Frank,

That's a very, very shitty quantum sensor. Almost as bad as the Specmeter versions. It's just as bad as lumen/lux/footcandle meters, re "spectral response" and being weighted for human sight, not plant growth. Check out the "quantum response", it's effing terrible!

I probably know more about these topics than all growers combined, with the exception of possibly KNNA.
https://www.icmag.com/ic/group.php?groupid=139

take a look around what meter do you see used by the local ag college or greenhouse operator

rives · Oct 7, 2011

spurr said:
I probably know more about these topics than all growers combined, with the exception of possibly KNNA.

Your humility is inspiring.

spurr · Oct 7, 2011

dankfrank said:
take a look around what meter do you see used by the local ag college or greenhouse operator

Any worth their salt use Li-cor LI-190SA or the 191. Read any plant study quantifying light and Licor LI190SA or the Kipp and Zonen brand (which isn't as good as LiCor) is used.

It's pretty obvious why the Apogee sucks so bad, it doesn't even count photons between ~650-700 nm and severely underweights photons between ~400-500 nm.

spurr · Oct 7, 2011

rives said:
spurr said:

I probably know more about these topics than all growers combined, with the exception of possibly KNNA.

Click to expand...

Your humility is inspiring.

I am very humble, I was merely stating a fact. That doesn't make me 'full of myself'. Would you accuse Einstein of not being humble if he said he was smarter than most people? (and no, I'm not comparing myself to Einstein).

It's a simple fact that myself, KNNA, wazzup and a couple of other people are on another level in terms of light quantum physics and photobiology. I am more focused on irradiance measurements (instantaneous and daily net), they are more for focused on radiance measurements (instantaneous). That's not arrogant or narcissistic, it's simply a fact. Just like it's a fact Microbeman is on another level when it comes to compost teas and microscopy.

rives · Oct 7, 2011

spurr said:
I am very humble, I was merely stating a fact.

Perhaps. Unfortunately, I think that you will find that any contribution that you wish to make is instantly and completely lost in the arrogance of your delivery.

spurr · Oct 7, 2011

I didn't mean it come across that way, and it didn't dawn on me that it could be construed that way. I will try to not come across that way in the future :ying:

spurr · Oct 9, 2011

I forgot to mention:

Every single 'light chart' (e.g., X inches for Y wattage, or by lumens or Lux) for cannabis growing I have seen is total bullshit hogwash. Mostly because we can't quantify light for plants as inches from lamp, lumens or Lux; and many of the charts (ex., the one from Skunk School [1]) are just made up bullshit. I have done much testing on cannabis with my quantum sensor, and I can state (nearly) as a matter of fact that we want:

~800-1,000 umol/area^2/second for veg, early-flowering and full-flowering (when daylength is > 10 hours)
~500 umol/area^2/second for seedlings (this produces VERY compact seedlings, no stretch and big leafs)
~100 umol/area^2/second for cloning

[1] Here are the bullshit charts from Skunk School, CaliGrower needs to stop posting such BS:

P.S.
Using zero nightlength per day (e.g., 24 hours of light per natural 'day') is never a good idea ...

spurr · Oct 9, 2011

Even worse than the shitty Skunk School charts are these ones using foot-candles!

rives · Oct 9, 2011

Spurr, I would like to find an economical meter to compare the output from my Lumigrow ES330 to a DIY fixture. I'm more interested in the comparative accuracy than absolute accuracy, if that makes sense. I have no intention of spending $500, much less $2700 - this is just a one-time measurement that I am interested in to quell my curiosity. Any suggestions?

spurr · Oct 9, 2011

@ All,

Here is data from a good study on cannabis with respect to rate of photosynthesis (Pn) from CO2, irradiance (quantified with LiCor LI-190) and temp. This screen shot is more about irradiance than CO2 and temp. Please note, this data was complied 60 minutes after the "light on event" (when lights turn on), once cannabis reached "steady state" photosynthesis, which takes ~45-60 minutes. Also, the data was complied using only red photons, not "white light" and no inclusion of blue photons. Thus, we would not want to use 1,500 umol/area^2/second all day, this has to do with a topic I have written much about: "Daily Light Integral" (DLI; https://www.icmag.com/ic/showthread.php?t=209952).

Note:
"Photosynthetic Photon Flux Density" (PPFD) is the same thing as umol/area^2/second, except PPFD has a defined area of a meter^2. Because many growers user smaller or larger than meter^2 canopy and irraidacne is not homogenous at canopy (unlike outside under the sun) I prefer not define the area. Thus, I don't use the term PPFD, I use "umol/area^2/second", which is the same as "umol/m^2/s^-1" as seen in the screen shot above, the only difference is I'm not defining the area.

spurr · Oct 9, 2011

rives said:
Spurr, I would like to find an economical meter to compare the output from my Lumigrow ES330 to a DIY fixture. I'm more interested in the comparative accuracy than absolute accuracy, if that makes sense. I have no intention of spending $500, much less $2700 - this is just a one-time measurement that I am interested in to quell my curiosity. Any suggestions?

Do you live close to a University or good College? You couple probably ask the Ag dept. head or other professors if they can test them for you. That way it's free and will be very accurate, that is, if they use LiCor (or better) brand quantum sensor.

Otherwise you could send them to me and I could test them for you and then send them back to you, if you pay for shipping. You could send one at a time so you're without both lights at the same time.

I am testing luminares (the scientific term for reflector, housing, etc.) for a brand new company marketing to cannabis growers. One of their luminares I am testing for them uses the most ideal position for an HID: vertically oriented HID in a horizontal reflector. The (or one of the) owner(s) come(s) from the lighting industry for non-horticultural use, so the lumainres haven't yet tested with proper quantum sensors (because light industry uses lumens and Lux and even FC). I am doing the testing for them, and I will give them input on how they can improve their luminares, at their behest. It's a great company with great luminares, I think they will be the future, at least the vertical HID in horizontal reflector should be the future of HID. And it's great they want my input and will considering redesigning aspects of the reflectors after I publish the data.

I will copy the work of Sanjay Joshi, Ph.D. and Timothy Marks (2003) from Advanced Aquarist, when testing the luminares for the new company. I could do the same testing for your LED arrays, that way you will know if yours is better than the commercial unit in terms of irradiance and homogeneity at various distances from LEDs. The only difference is I will use the terrestrial Licor quantum sensor (LI-190) and S.Joshi and T.Marks used the underwater Licor quantum sensor. I would prefer to use the underwater sensor but I cannot afford to buy one yet, the sensor alone is ~$800.

Analyzing Reflectors: Part I – Mogul Reflectors
Sanjay Joshi, Ph.D., Timothy Marks (2003)
http://www.advancedaquarist.com/2003/3/aafeature

Figure 3. Test Grid positioned on top of enclosure

Figure 4. Positioning sensor for readings

Figure 5. Licor Data Logger, Sensor and Attachment for holding sensor

rives · Oct 9, 2011

I appreciate the input and the offer, Spurr. I live way back in the sticks, but I am near UC Davis on a monthly basis, so that is probably an option. I understand that they have done a lot of testing on the Lumigrow units, and I assume UCD would have top quality test equipment.

I am quite curious as to how the two fixtures will stack up - my design is something that I came up with after much consultation with Knna. It uses (123) of the Golden Dragon Plus 660nm leds and (4) PL-L 55w lamps. It isn't finished yet, I'm still waiting on some parts, but my preliminary testing shows that that my cooling is capable of handling the led's at levels up to 600ma. Hopefully the wide dispersal angle of the GD+ lenses will complement the range of the PL-L lamps. Should be interesting.

Light meters--what rating do I need

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