Light meter questions. Beta team please?

What's up icmag I have a question I would like someone who knows more about lighting to answer. I bought a par meter from sunlight supply https://www.sunlightsupply.com/shop...ments/par-meter-with-remote-sensor-sun-system .Will this meter help me to balance the light in my room? In a post by beta test team I saw them reccomend either a better ($1000) meter, or a high quality lux meter ($150) plus calculations. I already bought this $400 meter a while back and I am simply looking to make my room (hps lighting) more uniform. I do not need 100 percent accuracy. Maybe beta test team can explain whether or not this meter will be useful for me. Also big thanks to beta test team for all the data they have been sharing and answering many questions throughout their threads.

That looks like a re-branded Apogee sensor with a price increase, as well. Looking at its accuracy (https://sunlightsupply.s3.amazonaws.com/documents/product/748205_Instructions.pdf) it's pretty much the same response as the Apogee.

If you don't need it to be very accurate in terms of irradiance (PPF), but rather accurate in terms of uniformity, that would work fine. If you wanted to use that for irradiance measurements (PPF) I would just make the same point as in the other thread: it's not accurate for HPS especially; but I have been thinking recently that with the lamp's SPD (digitized) the measurements from that sensor (or the quantum sensor) can be adjusted to be more accurate after the fact.

P.S. I'm glad the data we're collecting and sharing is helpful to you.

Thanks for the clarification. I will use this meter for uniformity for now until I have time to purchase and play with a better one. If I get the other meter, I will take readings with both to demonstrate what you have explained about their difference. Appreciate the quick response.

You're welcome. But I think I can save you time in comparing them, because after you posted this thread I did a little research and it seems Apogee (i.e. Dr. Bugbee) has done the comparisons for all the major quantum senor brands vs. his Apogee (which is what you have, I think); dating back to 2009 and 2012, but I only just now found them.

Anyway, it seems like the sensor you have, in a very ballpark value, for traditional HPS (not the DE or something like Hortilux SuperHPS), will show PPF around 5% to 10% below what PPF really is when using a perfect sensor.

In the words of Dr. Bugbee (owner of Apogee) and another researcher see the screenshot below. We have both the LI-COR LI-190 quantum sensor and an Apogee 3' line sensor using six Apogee SQ-120 quantum senors (the SQ-120 is for electric radiation, not the sun):


Here are the studies and other info, both about HID and LED luminaires in terms of accuracy of quantum sensors in general, and specifically about your sensor (which I think is a re-branded Apogee). It's important to note the Apogee work seems to use a T-5 florescent as the reference, while LI-COR uses a tungsten halogen (the latter is preferred).We're going to see if we can correct the inaccuracy of the PPF from your sensor type (Apogee) when accounting for the luminaire's SPD...now that we're finally back to working on our spreadsheet for radiation analysis (HISSA).

Oh yea, to anyone reading: Don't bother with SpecMeter quantum sensor, they're terrible; if you want a sensor but don't want to spend $600 to $1,000 for the LI-COR, get the Apogee SQ-120 sensor and a meter to show the PPF, or get MQ-200 model from Apogee (all-in-one).

pezthetoker said:

In a post by beta test team I saw them reccomend either a better ($1000) meter, or a high quality lux meter ($150) plus calculations.

Click to expand...

I just wanted to point out for the lux meter if you're only using it to find the irradiance uniformity of your footprint you don't need to do the calculations to which I referred, using lux as-is is fine.

The calculations are only needed to convert lux to PPF, but that's not necessary if you're only testing uniformity.

I am currently using hortilux super hps so this info is especially useful for me. While uniformity is my main concern, I will now also have a ballpark ppf to shoot for. If I remember correctly in your other thread you said that a good ppf to shoot for in a fully controlled environment was 700 umol. So I should shoot for 90 to 95 percent of that at my canopy along with the best uniformity I can manage? Thanks again I really appreciate your help.

You'd want to over-shoot your goal PPF by 5% to 10%, not under-shoot, because your sensor errors by showing less PPF than is really there. I think going 110% is a safe bet, even though closer to 105% may only be needed. So for 700 PPF (which is a good goal for vegetative and flowering stages), you'd want to use 770 PPF to reach 110%. But this is only a guesstimate because your lamps' SPD is not the same as tested in the works I cited.

To get a more accurate error correction factor than 1.1 (i.e. 110%) the lamp SPD would have be taken into account.

In terms of the goal PPF for plants, it's also about the total photons per day (as mol), which is more important than PPF (to plants) in many ways. Using common photoperiod for vegetative and flowering stages, PPF of 600 to 800 is optimal in most cases - greater PPF for flowering relative to vegetative stage is a good goal - to keep DLI high in flowering but not too high in veg, but is not easily achieved.

I know Gavita likes to claim 1,000 PPF is the goal for all growth stages, and therefore 65 DLI and 43 DLI is the goal for vegetative and flowering stages, respectively (DLI = PPF x photoperiod x 0.0036), but they have no sound reasons for making such a claim, only one study on Cannabis that itself was pretty flawed and can't be used for real-world irradiance goals. Also, 65 DLI is way too much DLI, even if it's not hindering the plants (which it likely is) it's way too much energy, serving only to drive up the costs of production. Also, by claiming 1,000 PPF is ideal Gavita gets to sell more units...greedy much I wonder?

Great explanation. You have given me a much better understanding of lighting with just a few paragraphs. Thanks once again. I wish I had some info that would be useful to you but instead I feel I would love to pick your brain in a few other subjects. You can message me if you would ever like me to send out a free glass spoon/pendant/dabber or something though.

Beta Test Team said:

You'd want to over-shoot your goal PPF by 5% to 10%, not under-shoot, because your sensor errors by showing less PPF than is really there. I think going 110% is a safe bet, even though closer to 105% may only be needed. So for 700 PPF (which is a good goal for vegetative and flowering stages), you'd want to use 770 PPF to reach 110%. But this is only a guesstimate because your lamps' SPD is not the same as tested in the works I cited.

To get a more accurate error correction factor than 1.1 (i.e. 110%) the lamp SPD would have be taken into account.

Click to expand...

Re-reading this, I think I did a poor job of explaining what I was trying to explain, and mixed up examples. Let me try again:

If we're assuming the senor's error correction factor (multiplier) for HPS is 1.1 (that is, 110%, because we're assuming the sensor is -10% inaccurate), and you are using the sensor to hang lamps using a known PPF goal, you would multiply the goal PPF by 0.9 like you wrote; so, in the case of 700 PPF as a goal, you would use around 630 PPF as the reading from your meter. But, when you are using the sensor to find the PPF at the canopy for example, you would multiply the PPF listed on the meter by 1.1 to find the 'real' PPF.

So two correction factors, 0.9 and 1.1.

Sorry for any confusion.