lux?
- Thread starter fishwater
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HydoDan
Well-Known Member
I did a search on your question..
A Lux meter (which measure lumens) is cheap and can be used in place of a PPFD meter when measuring the output of full spectrum LED boards. It is not 100% accurate as the conversion is an approximation but it is more than enough for planning out your grow room light spacing and deciding how high to hang your lights.
A Lux meter (which measure lumens) is cheap and can be used in place of a PPFD meter when measuring the output of full spectrum LED boards. It is not 100% accurate as the conversion is an approximation but it is more than enough for planning out your grow room light spacing and deciding how high to hang your lights.
ChemDogLover
Well-Known Member
Check out the Photone app
Keep in mind, phone apps are crap on Androids, to many different manufactures and light sensors.
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ChemDogLover
Well-Known Member
I did not know that, it’s decent in the iPhone
Parzival
Well-Known Member
You’ll be fine using a lux meter for LED’s—it gets you close enough. After all, these are just plants.
Measure the Lux and either multiply it by 0.015 to get a rough-ballpark ppfd, or you can use this webpage to convert it (if desired): https://www.waveformlighting.com/horticulture/convert-lux-to-ppfd-online-calculator
Measure the Lux and either multiply it by 0.015 to get a rough-ballpark ppfd, or you can use this webpage to convert it (if desired): https://www.waveformlighting.com/horticulture/convert-lux-to-ppfd-online-calculator
It's not always that easy, different conversions are needed for lights with UV, deep red and far red.
By the way, LED lights do not have IR.
Parzival
Well-Known Member
Shhh, don’t tell my plants. lol
Yeah, who cares if there is actually 25% more light than measured. After all, these are just plants, right?
Billy the Mountain
Well-Known Member
A $20 Uni-T Lux meter was both linear and within a few percentage points of a Apogee PAR meter when tested by MIgro.
More than enough accuracy for anything this side of NASA work.
I was able to borrow an Apogee MQ(?) 500 for a few days and 58000 Lux = 1000 ppfd for my lights; pretty much identical results to Migro's test.
More than enough accuracy for anything this side of NASA work.
I was able to borrow an Apogee MQ(?) 500 for a few days and 58000 Lux = 1000 ppfd for my lights; pretty much identical results to Migro's test.
Parzival
Well-Known Member
OP, don’t let people over complicate this for you. You do not need a par meter to use LEDs. A Lux meter will get you close enough. It’s also not measuring with a 25% error... Best part is that you can use a Lux meter to calibrate the Photone app, if that’s what you prefer. 
If you use the methods I posted above, watch how the plants respond and take notes. After a grow, you’ll know where to set the lights according to Lux for your particular LED light and environmentals.
If you use the methods I posted above, watch how the plants respond and take notes. After a grow, you’ll know where to set the lights according to Lux for your particular LED light and environmentals.
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If I had a lux meter, I'd use that instead of Photone on a $1000 iPhone. I tested Photone in early 2021 and then again in mid-2022. When I emailed the programmer, he relayed the difficult of getting good data out of Android. But even on an iPhone, I'd be leery. A light meter, esp with Bluetooth is a very solid approach but, if you want to take the time to set up the diffuser and then trust that your phone is one of the accurate ones…each to their own.
If you've got the $$, an Apogee will get you really close. For 1/20 of the prices of an Apogee + a wand, the Uni-T Bluetooth model will get numbers that are just as accurate in practical terms. The only place where the Apogee really…outshines the Uni-T is in low light. I haven't documented it but I think I noticed that at PPFD's in the < 300 range, the converted values from the Uni-T aren't that accurate. That's my recollection from a couple of grows ago — I'll run some numbers again. Regardless, the Uni-T Bluetooth rocks.
I own an Apogee and it's a great instrument. If I were starting over, I'd go with the Uni-T Bluetooth.
I've attached a document I put together that might be helpful folks who are using a lux meter and who want to convert lux to µmol.
If you've got the $$, an Apogee will get you really close. For 1/20 of the prices of an Apogee + a wand, the Uni-T Bluetooth model will get numbers that are just as accurate in practical terms. The only place where the Apogee really…outshines the Uni-T is in low light. I haven't documented it but I think I noticed that at PPFD's in the < 300 range, the converted values from the Uni-T aren't that accurate. That's my recollection from a couple of grows ago — I'll run some numbers again. Regardless, the Uni-T Bluetooth rocks.
I own an Apogee and it's a great instrument. If I were starting over, I'd go with the Uni-T Bluetooth.
I've attached a document I put together that might be helpful folks who are using a lux meter and who want to convert lux to µmol.
Grow Lights Australia
Well-Known Member
Our lights have a LUX to PPFD conversion factor of 0.022 at full power (5A). I am only stating this because if you use 0.015 you will get a 46% error. Our spectrum is not typical but it goes to show you cannot use a universal LUX to PPFD conversion unless you are using a universal spectrum. To get the conversion, divide PPF by lm.OP, don’t let people over complicate this for you. You do not need a par meter to use LEDs. A Lux meter will get you close enough. It’s also not measuring with a 25% error... Best part is that you can use a Lux meter to calibrate the Photone app, if that’s what you prefer.
If you use the methods I posted above, watch how the plants respond and take notes. After a grow, you’ll know where to set the lights according to Lux for your particular LED light and environmentals.
bigboerboel
Well-Known Member
Fishwater, I have a new PAR meter I'll sell you cheap. I bought one and two days later got the same one for my birthday. They work great. I love mine, and have adjusted my LED height and intensity settings according the PAR data I've read on this forum. e.g. 300-600 in Veg, 600-900 in flower. It takes the guesswork out for me.
Let me know.
Let me know.
Parzival
Well-Known Member
Thanks for taking the time to post all of this information. That percentage seems high to me, so I ran some numbers. I am not seeing a 46% error. Mind sharing how you got to that percentage?
With a 0.015 universal conversion factor, I'm calculating a 31% error in calculated ppfd for a light with an actual conversion factor of 0.022. Using the website I also linked with the original post giving the 0.015 conversion factor, I am only getting a 13% error when selecting 3000k high CRI LED. Via a back calculation, ~ 0.019 seems to be what the waveformlighting website is using as a conversion factor for those settings.
Looking at HLG's online LUX to PPFD calculator, I've back calculated these conversion factors for the following fixtures:
QB 648 Diablo Spectrum ~ 0.0163
QB 648 Diablo X Spectrum ~ 0.020
HLG Tomahawk Spectrum ~ 0.0180
Rspec FR Spectrum ~ 0.0173
QB 288 V2 Rspec ~ 0.0155
QB 288 V2 3000K ~ 0.0145
QB 288 V2 4000K ~ 0.0144
QB 96 Elite V2 ~ 0.0151
HLG's Calculator: (https://horticulturelightinggroup.com/blogs/calculators/converting-lux-to-ppfd)
The PDF above, posted above by Delps8, includes the following conversion factors:
CMH @ 3100 K ~ 0.0170
CMH @ 4200 K ~ 0.0154
Cool white flourescent ~ 0.0135
Dual Ended HPS ~ 0.0130
Mogul base HPS ~ 0.0122
QB 288 V2 3000K ~ 0.0146
QB 288 V2 4000K ~ 0.0144
QB 288 V2 Rspec ~ 0.0155
QB 648 Diablo ~ 0.0163
QB 96 Elite V2 ~ 0.0151
Sunlight ~ 0.0185
Vipar Spectra XS-1500 ~ 0.0145
Rapid LED Royal Blue Puck ~ 0.0130
Here's my math:
Estimated PPFD -> Row C = (Universal Conv. Factor) * (Measured LUX)
Actual PPFD -> Row D = (Actual Conv. Factor) * (Measured LUX)
Error% -> Row E = [ { | (Actual PPFD) - (Estimated PPFD) | } / (Actual PPFD) ] * 100
Of course there are a few exceptions, but a universal conversion factor of 0.015 seemed to get one right in the ballpark. For a lot of these fixtures, you're only a few points off the mark without any fine tuning/adjustments. For some of the newer fixtures with unique spectrums, just adjust the conversion factor to better fit the fixture. I imagine this should be good enough for the majority of home growers.
Calculations:
Viparspectra XS-1500 had an error of 3.45%, but I hit the max of 10 uploads so I didn't attach it.
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Rocket Soul
Well-Known Member
I can only guess but i think the 46% number would come from:
0.022/0.015=1.46
The gla spectrum creates 46% more photons than whatever spectrum that 0.015 number comes from, per measured lux.
Parzival
Well-Known Member
Yeah, maybe. But that seems to be measuring the difference between the conversion factors, not the PPFD.
Okay, if he's doing the calculation like that, it's in error, imo. It should be as follows: [ abs(0.022 - 0.015) / 0.022 ] * 100 = 31.82 %
The "abs" is just there to clarify that you want the absolute value of the difference between the two conversion factors and divide that by the correct conversion factor because that's what you're finding the error for: the amount of error created by the generic conversion factor when related to the actual lab-tested conversion factor.
I calculated the error percentage using the difference between the PPFD calculated using the conversion factor given by the vendor against the generic 0.015 and got this:
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Re. the 46% error - GLA didn't specify the direction of the error but it can be determined by doing the math on 15 vs 22. The variance is 350µmols which is 46% of 750. It would have been more clear to state it differently.
0.022 is freakishly high. That's due to the gobs of high red plus the far red, I'd assume.
All in all, it's an interesting spectrum but what's the impact on the plants. Bugbee has demonstrated what I refer to as the "blue photon" penalty where yield drops off when cannabis is exposed to > 4% blue in flower. That's one of the reasons why I went with separate veg and flower grow lights. Maybe they're seeing that terpenes and cannabinoids increase enough to offset the loss in yield?
Billy the Mountain
Well-Known Member
Parzival
Well-Known Member
But the error in 15 vs 22 is only 7. It doesn't make sense to relate the error to the generic value of 15, but instead it should relate to the 22. You're looking for the error with respect to the actual conversion factor, not with respect to the generic conversion factor.
[ abs( 15 - 22 ) / 22 ] * 100 = 31.82%