ppfd v lux readings. Help Me..

[f-e]

I managed to get this together


It's a chart of different light types, and how a lux meter would read at different ppfd levels. I would very much like to put a ppfd and lux meter together under some leds to add to this information. Ideally, under Samsung LM301 led's at 3k, as they seem by far the most popular choice. Does anyone have both meters and these leds? Perhaps even a couple of lux meters to repeat the test. Then all 3k lm301 users can use a lux meter to measure ppfd.

I know people here have a ppfd meter and leds. Even if different leds, the figures would be useful.

Edit: Perhaps someone can also use their meters to confirm my charts accuracy. It's just some ripped information, not my own work

 

[f-e]

Okay, I think I cracked it.
The LM301B is 0.52μmol/s at 65mA.
The LM301B is 220lm/w at 65mA.
2.7v x 0.065A is 0.1755w
220 x 0.1755 is 38.6lm

So if my hastily done maths is correct, the LM301B outputs 0.52umol and 38.6lm at 65mA.

So, whatever a lux meter says, you divide it by 75, to get the umol. When using the LM301B


I'm not sure how useful that is to me if I'm honest. It allows me to target the umol other people are using, with just a lux meter. But why would I copy someone else. I'm happy to see what works, then use my lux meter, to enable me to repeat that illumination level months later.

Hmm.. I just measured under a 400 and got 30,000 lux. Then set some panels at 30,000 lux beside it. Giving a calculated 375umol under the 400, and 400umol under the leds.

This is pure theory. A rushed set of thoughts as I'm heading for the door. I have never even looked at what umol levels work, so can someone tell me if I'm even in the ballpark?

edit: I thought the led was 0.2w so my 2.7v might be off, or the 0.1755 generally.

 

[SuperBadGrower]

Hey sounds like you got it already. You can also divide QER (µmol/j) by LER (hard to explain) and get the number you're looking for

These are from Stephen from HLG posted over at rollitup in 2015 or so

Cree COB 3000K 80 CRI 0.0144 (69.1)
Cree COB 3500K 80 CRI 0.0142 (70.2)
Citizen COB 3000K 80 CRI 0.0144 (69.4)
Citizen COB 3000K 90 CRI 0.0161 (62.2)
Samsung 561C 3000K 80 CRI 0.0145 (68.9)

This is what I found about lm301b from grower.ch

LM301B - A1/SK - 3000K @65mA

QER: 333.4 lm/W
LER: 4.81 µmol/J
-> 2.755 µmol/J

the QER/LER values are switched but 4.81/333.4 = 0.0144.

301h is pretty much the same as 301b.


Long story short, multiplying lux reading by 0.0145 or dividing by 70 should get you close enough

30k lux is good for veg, 55k for flower

 

[f-e]

Cheers buddy.
Looking at my charts, and crunching away on my calculator, I find the std mh column is just 1% different. So I (or anyone else) can just use that for the majority of white leds worth using.

I also use the 90cri citizen, which stands out from the crowd, but it's still only 10% off.

Thanks for the post. I imagine a few people will mull over this thread and realise they can measure ppfd now, with just a $10 lux meter.

 

[SuperBadGrower]

Hell yeah! When I found out that it works like this I immediately bought a lux meter
There are times when I still would like to have a quantum meter, but they are just way too expensive to justify such a purchase. Now you can even measure it with a smartphone! (I would recommend a dedicated meter that can measure the sun; I've seen that some apps stop at 50klux)

Ofc when somethings like 660nm, 390nm or whatever are added, these conversion numbers kinda lose their value... but that's a given

Damn... when I think about it, I would rather lose my EC/PH meters than my lux meter... it's just that useful. served me great with CMH too

 

[SuperBadGrower]

https://horticulturelightinggroup.com/blogs/calculators/converting-lux-to-ppfd

Here HLG provides a conversion rate for the Rspec which has the famous 660nm spike.
(lux)/64.55 or (lux)*0.0155

 

[f-e]

I'm not sure about their math tbh. The top bin 3000k led is listed between 38 and 40 lm by Samsung. I got 38.6 by my math, but call it 39. Divide by 75, is the 0.52 Samsung says. Not 0.56, which you get dividing by 70. Beyond the better lm301h's 0.54

Divide by 75 is easier on my brain. Shift the decimal place a couple, than add a third. So the 39 becomes 0.39 and add a third (0.13) is our 0.52

I think we are looking at colour shift. Where driving them harder is making them shift towards the red. So some of the visible red light is shifting out of the window we measure lumens in, but remains in the band measured for plants. So the lumen count drops, relative to the umol value. So while my math agree's with Samsung at 65mA, the HLG math is perhaps correct at ~180mA

It's all academic though. Anything within 5% (as we have here) is going to get us where we want to be. From there it's all about our individual styles.

I put it up to about 700 umol/s or 50,000lm which matched a new 600 over a meter. Give or take a lot more than 5%. Because holding a lux meter the same height is a task in itself.

 

[I'mback]

...buying the appropriate meter for what you are measuring is less hassle on the brain

 

[Guest]

@I'mback
I think the main argument is cost. If there is a formula for getting a ballpark distance with-out having to lay down some significant coin,
I'min.

This is uncharted territory for lots of us and by virtue of these forums we can learn from our collective trial and errors. Shit, this experimentation of ours may even advance some of the current knowledge or complications!

With that said I have the Dr. Meter cheapo lux meter. I can adjust the setting from 1x lux (the 2000 setting) to x10 lux (20000) to x100 lux (100,000).
Which setting should I have it on for our testing LED inside a tent?
Also do you think closing the door of the tent ( and not being in the tent) is necessary when testing?

 

[I'mback]

@I'mback
I think the main argument is cost. If there is a formula for getting a ballpark distance with-out having to lay down some significant coin,
I'min.

This is uncharted territory for lots of us and by virtue of these forums we can learn from our collective trial and errors. Shit, this experimentation of ours may even advance some of the current knowledge or complications!

With that said I have the Dr. Meter cheapo lux meter. I can adjust the setting from 1x lux (the 2000 setting) to x10 lux (20000) to x100 lux (100,000).
Which setting should I have it on for our testing LED inside a tent?
Also do you think closing the door of the tent ( and not being in the tent) is necessary when testing?

You don't have to break the bank to get one. If you want a meter that dances like a seal etc, then....

https://www.amazon.ca/Hydrofarm-LGB...ofarm+LGBQM+Quantum+PAR+Meter+Micromol+Sensor
Got mine off e-bay for $100 and change. Works like a charm

 

[SuperBadGrower]

I think those hydrofarm units are just overpriced lux meters which apply a conversion rate similar to how PPM pens are EC pens. But I'm not sure

Here bruce bugbee explains what real quantum sensor is made of, I doubt this is within those.

https://youtu.be/Pc_tqLYhITA?t=715

11:55 onwards

edit: or possibly they have some light filters inside. You can make a cheap ghetto PAR meter out of a lux meter by opening the sensor and covering certain lighting filters (used for photography or theatrical lighting, I forget which) over it. Anyawy, I seen the hydrofarm tests and it's not accurate enough compared to an apogee to warrant the extra $80 over a lux meter - just my 2 cents.

 

[I'mback]

I think those hydrofarm units are just overpriced lux meters which apply a conversion rate similar to how PPM pens are EC pens. But I'm not sure

Here bruce bugbee explains what real quantum sensor is made of, I doubt this is within those.

https://youtu.be/Pc_tqLYhITA?t=715

11:55 onwards

edit: or possibly they have some light filters inside. You can make a cheap ghetto PAR meter out of a lux meter by opening the sensor and covering certain lighting filters (used for photography or theatrical lighting, I forget which) over it. Anyawy, I seen the hydrofarm tests and it's not accurate enough compared to an apogee to warrant the extra $80 over a lux meter - just my 2 cents.

Bottom line it gets the job done. It doesn't matter what it reads really, providing its a measurement "you/one uses" as a reference throughout ones grow and subsequent grow etc....

I bought mine instead of buying a bluelab PH meter.

So do I want to take a reading, head out to the PC do a bunch of math, or take a reading and adjust accordingly. Its a no brainer to me. OTOH whatever float peoples boat.

 

[f-e]

I have a lux meter with similar scale. The orange sided one. I just have it across in the x100 position. I left my lights measuring 500, which on a x100 scale, is 50,000 (which they were too tight to give us a bigger screen to display). I now know that at 500 on my meter, it's 50,000 lux and that amounts to around 700 umol/s. This newer measure, widened my search results, to where I learned this is about 75% on the grow throttle. So I'm happy with that. 75% of maximum plant performance seems like a worthy struggle for a relative newbie. I will start there. 500 on my meter. 700 umol/s on a fancy one. Two numbers I can about see along a ruler.


Oh this is fucking awesome. 500/700 are the ec conversion numbers. Got a truncheon? They are side by side scales. 500 is wrote on the meter, beside 700. It's the lux to umol cheat sheet, right on the cf truncheon. It says, 840umol/s will display as 600 on my cheap meter. That is as high as makes sense, and the absolute maximum 1500umol/s isn't measurable for us, as our screen is a 999 count, which is 1400umol/s. According to my truncheon.

I can read these numbers off all day long. That's fucking great.



edit: Arr shit. I just seen a great big hole in this. Another conversion is needed. I probably can't measure the lux from an led panel. Many lux meters just measure green, and think it's the sun, so all the colours will be as bright. If you just measure the green portion of led light, it's not as strong as the blue or red.

And it was going so well https://www.apogeeinstruments.com/how-to-correct-for-spectral-errors-of-popular-light-sources/

 

[SuperBadGrower]

Probably replying too quickly here because I have to go in 5 minutes but I don't know how an EC meter made its way into this . There are different conversion factors to go from lux→ppf because there are different light sources which dont all give the same lux reading. There isno big hole, everything you need is already written out on the internet.

Unless you're talking about discrete diode leds which put out purple light - for those it's impossible because some may have more green diodes than others, while white PC converted leds all have about the same spectrum (which is why you can use *0.0145 for 4000K leds whether they are made by samsung or whoever and still be reasonably accurate)

 

[f-e]

I will have another go

The truncheon is a row of lights, beside each is written a value. Here is a chart.
https://blog.onestopgrowshop.co.uk/wp-content/uploads/2013/08/EC-CF-PPM-Comparison-Chart2.jpg
You will have to click the link to see the cheat sheet printed on the truncheon.
The last two columns are of interest to people that own a truncheon and also the lux meters that scale by 100.
These cheap meters display 500 when the given conversion factor of /70 tells us it's 700umol/s. As written on the truncheon.


The hole in this, is that our canopy might be at 50,000lux, but our lux meter can't measure it. I can stick my meter in there, see 500 (x100) on the display and read off that is means 700umol/s. But I would be wrong, as it wasn't 50,000lux. There is a discrepancy of up to 15% when using a lux meter on our leds and not sunlight.

The link in my last post shows how far off a lux meter is from the truth, when using different light sources. We need to apply a suitable conversion factor to the lux meters reading, to get the real lux. Only then can we divide by 70

I'm in a rush to.. Chat later.

 

[SuperBadGrower]

I will have another go

The truncheon is a row of lights, beside each is written a value. Here is a chart.
https://blog.onestopgrowshop.co.uk/wp-content/uploads/2013/08/EC-CF-PPM-Comparison-Chart2.jpg
You will have to click the link to see the cheat sheet printed on the truncheon.
The last two columns are of interest to people that own a truncheon and also the lux meters that scale by 100.
These cheap meters display 500 when the given conversion factor of /70 tells us it's 700umol/s. As written on the truncheon.


The hole in this, is that our canopy might be at 50,000lux, but our lux meter can't measure it. I can stick my meter in there, see 500 (x100) on the display and read off that is means 700umol/s. But I would be wrong, as it wasn't 50,000lux. There is a discrepancy of up to 15% when using a lux meter on our leds and not sunlight.

The link in my last post shows how far off a lux meter is from the truth, when using different light sources. We need to apply a suitable conversion factor to the lux meters reading, to get the real lux. Only then can we divide by 70

I'm in a rush to.. Chat later.

Right I get it, using the truncheon like a trick that's neat. I've done this thing so often that I know the numbers by heart so it didn't occur to me. (All these tricks are useful to know if you build your own lights)

Actually, the last link you posted from apogee shows correction factors for different quantum sensors, the expensive ones. Different models from Apogee and Licor have slightly different characteristics which means they are not entirely accurate in some regions. those 2 companies are like the Apple and Microsoft of quantum sensors

For example you can get Apogee SQ sensors for about $150 which work pretty fine under white leds. Under purples they don't do as well because they are not as sensitive to some far red bands.

Then there is newer MQ-500 I believe, I'm just writing this model number from memory. They are $300 and really capture the full PAR range accurately.

So, tanks to their conversion rates you can use an inferior cheaper model and still get quite accurate readings.

I can stick my meter in there, see 500 (x100) on the display and read off that is means 700umol/s. But I would be wrong, as it wasn't 50,000lux. There is a discrepancy of up to 15% when using a lux meter on our leds and not sunlight.

You are overthinking it now. The different conversion rates for different light sources are already account for the fact that light sources give different readings.

E.g. to convert sunlight to ppf you use *0.0185

If you treat your 3000K led like the sun:
30.000 lux = 555 PAR reading

However if you use the normal conversion rate:
30.000 lux = about 450 PAR reading

or HPS:
30.000 lux = 390

Really, there is only one issue about this whole thing to keep in mind: All the cheapass lux meters we use are not equal. You cannot trust the measurement. If the measurement were 100% accurate, all the conversion rates will definitely give accurate PAR readings.



A PPM pen is not a lux meter, but when I tested a very commonly used one in EC 1.4 calibration fluid, the result absolutely shocked me. It wasn't anywhere near 0.5 or 0.7. As you know EC→PPM goes on a scale of .5 or .7, thats just how it goes. If you used that pen (.....I used that pen....) you'd be overfeeding by 33% every single time.

I mean How hard can it be to make a damn PPM pen haha. They are just conductivity meters using the same kind of sensors and there are only 2 possible things to do with the reading. Somehow, they still manage to fuck this up. I really thought that this technology would be so basic that you can't go wrong. I can see similar things happening with lux meters. The idea, however, is that they are all the same.

If you wanna check your meters accuracy I suppose you could find a chart of the sun's intensity at some point in time and space. E.g. 1 may 12:00 108.000 lux reading at Stonehenge or something.

 

[f-e]

Hours of reading reviews, shows quantum meters are little more accurate than lux meters. And that's only in the extreme examples, at low light levels. It's a nice idea, but only the same meters measuring the same leds can give comparable results. Otherwise you must accept a 15% margin of error when reading peoples papers.

There is an interesting article about the London underground team swapping to leds. They couldn't prove they met the minimum illumination standards, and nobody could prove they didn't. Only an led manufacturer could really calibrate a meter for a specific led. Much as I was only going after the LM301b.

The sensible option, to compare with other people, is to use what they use. Which is usually the $10 type. Let that get you somewhere close, then as always, let the plants guide you. Any meter will help you repeat what you find, or balance your lights evenly over your space.

I can't wait to get them all sharing a dimmer. But that's another thread.


Good talk. You can add me to your friends list, any time you feel fit

 

[SuperBadGrower]

There is an interesting article about the London underground team swapping to leds. They couldn't prove they met the minimum illumination standards, and nobody could prove they didn't. Only an led manufacturer could really calibrate a meter for a specific led. Much as I was only going after the LM301b.

Oh, that sounds really interesting, I would love to read this one some time if you can find it!

The sensible option, to compare with other people, is to use what they use. Which is usually the $10 type. Let that get you somewhere close, then as always, let the plants guide you. Any meter will help you repeat what you find, or balance your lights evenly over your space.

Yep well said ... the most logical conclusion

Think we touched on most everything by now hehe. I encourage everyone reading to try it. No joke, the light meter is responsible for the biggest improvements to my growing and some eye opening revelations

This is the one I use, a small step up from the cheapest ones. A pretty solid unit. Obviously I can't speak to its true accuracy so I don't like to go out recommending it. Recently saw a light problem diagnosed with a phone lux app, actually - seemed pretty accurate... the tops were getting >1200 ppfd in veg and the plants were showing it.

 

[Horselover Fat]

I've tried a couple of phone lux meters, but they only go upto 10k lux.

 

[SuperBadGrower]

I've tried a couple of phone lux meters, but they only go upto 10k lux.

That's pretty low. I guess your particular phone can only measure to 10k. For all phone-related intents & purposes that would probably be OK. Deffo seen 90k+ readings so it is possible!

I'll A/B my phone and lux meter some of these days when I'm bored. Will post the results