Watts vs PPFD: which do you use?
- Thread starter The70’s
- Start date
Do I have this correct?
1,000 μmol/s/m² × 18 hours per day equals a DLI of 64.8?
EDIT: But, at 12 hours per day, it requires 1,500 μmol/s/m²? That seems... like quite a bit of light.
1,000 μmol/s/m² × 18 hours per day equals a DLI of 64.8?
EDIT: But, at 12 hours per day, it requires 1,500 μmol/s/m²? That seems... like quite a bit of light.
Delps8
Well-Known Member
Yup.
nmols X hours X 0.0036 = mols per day AKA “DLI”
Are you running that light level?
I understand the EC meter analogy - that measurement can be done with a DVOM and a calculator; and the "TDS" meters simply perform the same measurement and then multiply the result by one of three conversion factors, the specific one being left to the manufacturer to choose. Which, in theory, coincides with the one electrically conductive dissolved solid in the solution. Which is why they're never accurate in our application - our nutrient solutions contain multiple conductive ingredients. But I digress; I agree that both do the same measuring, and that the latter just obfuscates said measurement by doing simple math.
However a PAR meter (well, its sensor) measures a specific portion of the visible light spectrum. If I understand how the things work, a lux meter/sensor measures a portion of the visible light sensor that is slightly different (although there is a lot of overlap). I think its sensor is somewhat more simplistic than a PAR sensor, but I'm not sure ( @Icemud might have mentioned something in that regard, but my headache is fierce enough right now that I've got one eye shut, and am not thinking well). The ePAR sensor, I think, would be comparable to the PAR sensor in construction, but designed to measure yet another chunk of the spectrum, one that is close to that which the PAR sensor does, but extended slightly at the top end. I really need to go back, tomorrow, and retread Icemud's posts. I think... the PAR and ePAR results are... not weighted? But the lux meter weights is results; not a simple multiplication by a conversion factor, but kind of a bell curve. So the difference in result shown is more involved than the difference between an EC meter and a "TDS" one - and, unlike those two devices, these light meters are not measuring the same thing to begin with.
Er... I think. Or what passes for thinking right now.
Delps8
Well-Known Member
An EC meter measures conductivity. It can then display that result to indicate the PPM of a solution of sodium chloride that would have the same conductivity (the 500 scale) or a solution of potassium chloride (the 700 scale). And it's way off from the elemental values. And that's fine because, right out of the box, EC meters are only accurate to 0.1 EC. I see that when I "calibrate" my Bluelab EC pen and my Bluelab monitor. These are the notes in my Excel Feed Sheet document
"Blue lab monitor reads 1400 against a solution at 1385
Blue lab pen reads 1340 instead of 1385"
So they read 60 PPM different but they're both within the manufacturer's tolerance.
ePar reads 400 to 750 nm versus "standard" PAR of 400 to 700.
To put it bluntly, IDFK. I'm not currently doing so, but hope to start gardening again in a month or so. My intentions are to use my grow tent - a 100 cm × 100 cm Mars Hydro, so that's an area of one square meter (~10.764 square feet). It's also listed as being 39" × 39", but I assume that's due to lazy rounding. If not... 10.5625 square feet.
I have a brand new light to use in there. The company does not pay to advertise here, so I cannot post a live link. But if you, Icemud, and/or anyone else wants to take a look at the company's web page for it - specifically, the PAR maps published there - and tell me what I've got (lol) , and make recommendations vis-à-vis power level and hanging height, I would greatly appreciate it.
The light is an LED panel. AC Infinity IonBoard S44. I could have gotten the S33. When trying to decide, I sent an email to the company's contact address and the smaller one was recommended, but... The S33 is advertised for a 3'×3' space, and it - like most of them - suffers a good bit of drop-off near the perimeter of its advertised coverage area, and my tent is slightly (19.6%, so more than slightly, really) larger than 3'×3'. That S33 is only a 240-watt device. The S44, on the other hand, is a 400-watt light. It uses the usual Samsung LM-301B diodes, by the way (IDK about the red ones). It also appears to have serious dropp-off near the perimeter of its advertised coverage area - but my thinking was, I get the one that's meant for a larger area, and that won't be an issue, lol. Physically, it's just under 2'×2' in size, and its diodes are not evenly spaced (denser near the corners than in the center, although there's still a major bright spot under it, and it still fades at the edges, so...).
And IDK. I'll be growing autoflowering plants, so either 18 or 20 hours of light per day. NO supplemental CO2. However, the temperature will be miserably hot (easily 90°F, probably hotter), so the plants should be able to process the maximum amount of light-energy that a cannabis plant is capable of processing at "normal" levels of carbon dioxide. I was thinking that I might be able to get by with running the light at 80% power level? I'd like to run it at 20%
- or at least no more than 60%, but IDK whether that will be adequate? The dinner only has 20% adjustment steps, so my choices are 80, 160, 240, 320, and 400 watts.I also anticipate problems with the electric bill, so I really don't want to run it at more wattage than I need to.
Again, I cannot post a link to its web page. But a Google search for
Code:
AC Infinity IonBoard S44shitty. maybe opened a bit of a can of worms. the sensors the ppfd / lux / par / meters use have definitely advanced from when there were just 'par' meters only. however the current modern meters only measure 'par' and the rest is an algorithm. essentially all the same meter.
edit : you do pay more for it to be trusted and acurrate
edit : you do pay more for it to be trusted and acurrate
Smokey0418
Well-Known Member
yes that is correct , low 900 ‘s in the middle were it’s the strongest for me.
I had flowers 6 inches taller around the edges and one would think that it would be higher closer to the light but the bar design once you leave the Center is starts to fade to the sides and these flowers would see approx 6-700 μmol.
This is were I start thinking the fc6500 could very well be a better fixture as the extra bar could increase the umoles along the side.
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The70’s
Well-Known Member
whats the difference between 24” and 36” from the canopy if both distances are 300par. I do know the 36” distance will require more power from the wall, just wondering……
Smokey0418
Well-Known Member
Tent zipped up 34 inches my fce6500 would do 300 at 1/2 way between 50/75.
At 24 inches about 54%
And then the set it and forget it for now is 400 , so at 24 I’ll call it 68% as my plants now have a few leaves and I’m just looking for some momentum.
Those figures look about right to me from when I did the calculations years ago....
From when I was reading a lot of light research, the sun puts out around 2000 umol/m2/s-1.
Chandra also did a study, that showed that photosynthesis plateaus around 1500 umol/m2/s-1 but this rate is also determined by 2 other factors, temperature and available CO2. Therefore if you are not running co2 supplementation the benefits from pushing from around 1000umol to 1500umol are extremely minimal because the plant can't use the extra photons without extra available co2...
Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions - PubMed
Effect of different photosynthetic photon flux densities (0, 500, 1000, 1500 and 2000 μmol m(-2)s(-1)), temperatures (20, 25, 30, 35 and 40 °C) and CO2 concentrations (250, 350, 450, 550, 650 and 750 μmol mol(-1)) on gas and water vapour exchange characteristics of Cannabis sativa L. were...
pubmed.ncbi.nlm.nih.gov
So essentially a target of 1000ppfd in 12/12 is ideal without additional co2 supplementation, but 1500-2000ppfd would be beneficial only if using additional CO2.
Delps8
Well-Known Member
As hang height increases, you need to use more power to get the same number of photons to the plants, as you've stated, and the light pattern changes, as well. One cause for that is the light itself - the photon stream from the light spreads out and you get's more even. If you're in a tent, the photons bounce off the walls of the tent.
Head over to ppfdcharts.com and checkout some of the PPFD maps. Good example - look at any of the HLG lights and then look at a Migro array or the Spider Farmer SE-7000. The HLG lights use LED's on boards. That's an older design and one of the results is hot spots. The Migro or Spider lights are a newer design and they have a very even light pattern. "Uniformity" is the keyword.
I just looked at the PAR maps for that model... and based on what I see:To put it bluntly, IDFK. I'm not currently doing so, but hope to start gardening again in a month or so. My intentions are to use my grow tent - a 100 cm × 100 cm Mars Hydro, so that's an area of one square meter (~10.764 square feet). It's also listed as being 39" × 39", but I assume that's due to lazy rounding. If not... 10.5625 square feet.
I have a brand new light to use in there. The company does not pay to advertise here, so I cannot post a live link. But if you, Icemud, and/or anyone else wants to take a look at the company's web page for it - specifically, the PAR maps published there - and tell me what I've got (lol) , and make recommendations vis-à-vis power level and hanging height, I would greatly appreciate it.
The light is an LED panel. AC Infinity IonBoard S44. I could have gotten the S33. When trying to decide, I sent an email to the company's contact address and the smaller one was recommended, but... The S33 is advertised for a 3'×3' space, and it - like most of them - suffers a good bit of drop-off near the perimeter of its advertised coverage area, and my tent is slightly (19.6%, so more than slightly, really) larger than 3'×3'. That S33 is only a 240-watt device. The S44, on the other hand, is a 400-watt light. It uses the usual Samsung LM-301B diodes, by the way (IDK about the red ones). It also appears to have serious dropp-off near the perimeter of its advertised coverage area - but my thinking was, I get the one that's meant for a larger area, and that won't be an issue, lol. Physically, it's just under 2'×2' in size, and its diodes are not evenly spaced (denser near the corners than in the center, although there's still a major bright spot under it, and it still fades at the edges, so...).
And IDK. I'll be growing autoflowering plants, so either 18 or 20 hours of light per day. NO supplemental CO2. However, the temperature will be miserably hot (easily 90°F, probably hotter), so the plants should be able to process the maximum amount of light-energy that a cannabis plant is capable of processing at "normal" levels of carbon dioxide. I was thinking that I might be able to get by with running the light at 80% power level? I'd like to run it at 20%
I also anticipate problems with the electric bill, so I really don't want to run it at more wattage than I need to.
Again, I cannot post a link to its web page. But a Google search for
... should list it at near the top of the search results. If I'd had to pay for it, I would have bought from one of the forum sponsors, so I could post links,, upload PAR map images, and ask questions on the sponsor's thread. But... well... If I'd had to pay for a light, I wouldn't have been able to get any. It was a gift from someone who wants me to grow. . . .Code:AC Infinity IonBoard S44
a DLI of 65, on a 18/6 lighting would break down to approximately 1128 umol/m2...
So for your tent which is inbetween a 4x4 and a 3x3 (I think I got that right), and based on their PAR charts, I would probably hang the light 14-18" from the canopy. 12" looks like it would be too close as the center is almost at 2000umol. 14-18" seems to be the sweet spot where the middle would be getting above ideal lighting, and the sides would be within an acceptable range for 18/6 schedule...
I would probably start at 14", and if I saw the plants reacting badly or bleaching then I would raise them, but at 14 you should be fine pending the sides get full illumination with the panel being so close. (this would be at 100% output) based on the supplied PAR charts. Even at 14" you probably could get away with running the light at 80% and still be within the acceptable "max photosynthesis" range.
Delps8
Well-Known Member
Thanks for confirming that. I've been loathe to run that high. Yup, I read all the shit I can find and have a $500 light meter but sometimes I need a nudge (or more).
I did crank up my Growcraft yesterday - 255 watts to 311. My driver is in the tent (I'm in an unheated garage so I needed the heat when I started this grow) and the temps rose in the mid-80's pretty quickly so I had to turn it back down. This weekend, I'll move the driver out of the tent and ramp it up again. And if they get light burn, I can blame you, right? ;-)
Light falloff is a pain. Some lights handle it really well but, pardon the pun, I suspect that it really is "an edge case". My thinking there is that most growers don't have a lot of plants growing in the periphery of the tent and, if you're in a commercial grow, there are no "edges" - it's just rows of plants with lights above them.
600-700 µmols is still good light but I'm on board with wanting a uniform cast of light for the plants.
If you're topping your plants, as I do, where do the plants grow? Well, not in the middle because I've cut out the apical stem. The stems grow in a circular pattern which means they grow toward the outside of the tent.
Check out my reply to The70's above. That site was a real eye opener for me. Of course, there are other sources of similar info but that site's doing a bang up job.
Mars makes some good lights, no question about that, and we're getting more and more choices every day. One new light that's worth a look is from Atreum. It's for a 2' x 4' space but there's no reason why you couldn't run two, side by side.
Just for a chuckle, I've attached the PPFD map from the Kind LED I bought in 2017.
they still mix and match components. the biggest whine is they will advertise one set of components and ship with another. they're ok if what comes out of the box is the same as you pay for.
dual lighting is sometimes better than a large single.
Delps8
Well-Known Member
That's very bogus. Not bait and switch, technically, but not far off.
Switching from Meanwell to in house is not out of the kindness of their heart.
Yup. Redundancy is a small piece of it but there can be a lot of value in being able to change hang height easily.
Mayne
Well-Known Member
which, is crazy, seeing outside CO2 is only 400
Mayne
Well-Known Member
110 watts at 23 inches from light
a lot of times the secondary component is just fine. but yeah, technically grade 2.
plenty of times they will spec mean well hlg but ship with an elg, which is perfectly acceptable, and even a superior driver in some instances, but it is the lower priced quality mean well, reducing manufacture costs as much as 8 - 10 %.
at other times pairu winds up in the product. i've seen them extend lines with grade 2 components while new ones are in development. sometimes they change the original advertised spec, other times not so much.
the chipset is another crucial area i've seen not show up exactly spec.
it's like a box of chocolates ..
i run my entire grow at 24 inches but use active dimming all through. when the canopy hits 18 inches i raise the rig - actually i shelf grow and lower the floor but same same lol
i over light and use dimming. i also do a big jump in light from veg to flower, going from 200w to 600w, 4 cob rig to 12 cob rig.
edit : in full disclosure i should add i used to build and sell led led rigs before there were a flood of commercially available products. mostly cob. i don't anymore. i also used to work in show production lighting.