Light meters--what rating do I need

[Harry Gypsna]

Hey there.
Spurr, are you saying the lux meters are no use at all? I havent got the money for anything very expensive, and it would only be used to get my lighting evenly spread out and place my vertical walls of bud the right distance from the lamp.
While I understand that lux isnt a horticultural measurement, I figured it would be useful for this, and I know a few others have used them for setting up a vert.

 

[spurr]

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.

Hell yea! UC Davis is one of the best (if not THE best) Ag and Hort Uni's in the whole US, and the world. I bet my bottom dollar if you ask nicely they will oblige.

 

[spurr]

Hey there.
Spurr, are you saying the lux meters are no use at all? I havent got the money for anything very expensive, and it would only be used to get my lighting evenly spread out and place my vertical walls of bud the right distance from the lamp.
While I understand that lux isnt a horticultural measurement, I figured it would be useful for this, and I know a few others have used them for setting up a vert.

I wouldn't say they are no use at all, but their use is limited. It's better than nothing, ex., it's better to use a Lux meter than going by X inches for Y watts. As I wrote above, shoot for ~80,000-100,000 Lux (or higher, ex., for short days).

The problem with Lux and lumens and footcandles is they give more 'importance' (i.e., weight) to green light than to red and blue light. Thus, you do not get a true measure of photons plants use for photosynthesis and other photobiological reactions. Ex., using a Lux meter it could show a green LED array provides greater irradiance than a LED array with blue and red diodes, and we all know that isn't reality wrt plant photobiology.

In the future I plan to test many HID lamps and luminaires (reflectors/mogul/etc), as well as LED arrays, and I will report my findings publicly. That way anyone can make a more informed decision wrt lamp distance and luminaire brand (as HID or LED).

 

[spurr]

@ rives,

IIRC LEDgirl borrowed a Licor LI-190SA from a professor at UC Davis some time ago, to test her LED arrays. Sadly, she had no effing clue as to the proper use of the quantum sensor, so the data she reported was highly skewed and flawed. I tried to explain to her why she was wrong, but she just got mad and deleted all my posts.

You may have luck contacting LEDgirl at her web site and asking her from whom she borrowed the Licor LI-190SA quantum sensor and Licor LI-250A light meter. Then you could contact and ask that same person if you too may borrow the sensor and light meter (i.e., LI-250), or if not, then that person may be willing to test for you. It's a shot in the dark but you may hit bulls-eye

Just be aware LEDgirl has a huge ego that is not matched by her knowledge and intelligence. So maybe placate her a bit to get what you want ...

 

[rives]

Spurr, I appreciate the thought, but I would sooner throw myself on my screwdriver than ask LEDGirl for anything! Besides, I think that I have made enough posts about her products, warranty, design, and business practices that I would have to follow her lead and use a sock puppet as an intermediary. I think that I will try and contact Lumigrow and ask them who their contact was.

 

[Weezard]

Kiss it.

Kiss it.

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?

Oh.
You just want a rough comparative, yah.

While the proof IS in the budding, it's good to take a few clues to the party.

The red-necked simple method will give Spurr the horrors, but;


Done laughing?

I don't need details of what's wrong with using a radiometer.
I know the details.

I actually did use it with a li'l optical tachometer that I had lying around.
Was surprised at how close it tracked with my working meter;




It's inexpensive, available on-line, and will do a comparative measurement of the two lamps without a second mortgage.

Please stand down Spurr.
Not in need of furthur edumacation here.
I understand quantum, PAR, yada yada, I jus' nokea!

It's a lot of mathsturbation to me.
Don't mean shit to a tree.

No gotta work dat hard.

So, after some very rough, (but adequate for my purpose), readings, I grow meds!

That's the bottom line.

Got big, tight, buds at harvest?
I'm good!

Aloha, y'all

Weezard

 

[rives]

Love the Bubba approach, Weez!

 

[spurr]

Hey bra

The red-necked simple method will give Spurr the horrors,

The horror!

Please stand down Spurr.
Not in need of furthur edumacation here.
I understand quantum, PAR, yada yada, I jus' nokea!

It's a lot of mathsturbation to me.

Haha. I know you're really typing with one hand ... and the other hand is, um, erm, busy (shall we say ).

Don't mean shit to a tree.

That is the only part I where don't agree with you, it does mean A LOT to plants and trees [1]. There are ideal ranges for irradiance that will give bigger yield, better growth, etc. Providing too much light is as bad as providing too little light, that is why it's important to use correct light measurements for plants. While "close enough" is okay for horse shoes and hand grenades, it's not okay for plant irradiance.

No gotta work dat hard.

It's just as simple to use a quantum sensor as a Lux meter, fwiw. The cost of a good quantum sensor and data reader is the only sticking point for most people. And what I find odd, is most people spend more on booze and/or cigarettes (and porn!) per year than it would cost to buy a very, very, very useful quantum sensor. Not only that, but the benefits from a quantum sensor wrt saving money and making more money, wrt plant growth, electric usage (e.g., too much light is waste of money), yield, etc., can pay for the quantum sensor in one harvest (or a couple of harvests depending on skill and grow size).

Got big, tight, buds at harvest?
I'm good!

IMO, the real question is: can you get bigger, tighter buds at harvest? And that's where a quantum sensor can help.

Aloha, y'all

Weezard

Aloha nui loa bra.


[1] After living on Maui and Kauai for so long I can't hear or read the word "tree" without thinking about the number "three" ... LOL. Weezard and other Hawaiians will get the joke.

 

[Weezard]

"IMO, the real question is: can you get bigger, tighter buds at harvest? And that's where a quantum sensor can help."


Well, I don't disagree.
Just not for me.

No wanna win a prize.
nevah gonna amortize.

Only need 2, got mo' dan tree
An' I only grow da kine fo' me

Aino spend on booze n butts
Quite happy with white widow cuts

I sloppy, n lazy, sure. And yet.
My buds be good as dem kine get.

I bus' a law an' dis all gone.
But you sellum guys jus' carry on.

Skirting da law 'tween love and trust.
Scary-ass bidnis, but somebody must.

So I an' leave it at dat.

Aloha allovaya,
Weeze

 

[spurr]

Ha, wow, you're a poet! That was really well written and made me smile a few times. You sir, are indeed a wordsmith.

 

[knna]

For positioning a lamp and check it's degradation rate, any cheap lightmeter is valid.

I suggest to use one with range up to 200Klux (20000fc). One up to 50Klux may be used, but it saturates if you try to measure close to the lamp. For quick measurements, I use the Dealextreme.com model, up to 200Klux with decent accuracy (error is only noticeable on the blue range, and not excessive), probe not integrated and cosine corrected. Less than 30$.

As far as you check degradation taking care of positioning lamp and meter always at same distance and position, its fine. For positioning the lamp, you just need relative figures, so any lightmeter works for that.

 

[spurr]

Hey Knna,

How ya been? I hope things are good over there in beautiful Spain

I do want to point out that using a Lux meter is not a good idea for lamp positioning (as well as degradation rate), the problem (as we know) is that that photons are weighted for human sight, not plant growth. That means you do not get a true measure of the irradiance (which the plant uses). Thus, you don't get a true measure of how you far the lamp should be placed from the plant because 1 Lux does not equal 1 umol/area^2/second; and because every lamp has a different spectral quality (due to age, temperature, input power, etc.) which affects the Lux reading, but not the reading from a good quantum sensor. Also, all scientific data wrt cannabis and irradiance is (correctly) by PPFD, not Lux (besides that one old study I found), thus growers don't have proven values of Lux for best plant growth wrt rate of photosynthesis.

The main point is we cannot use a Lux meter to correctly and ideally position a lamp, due to the reasons I wrote about above. That is why a quantum sensor is the only real option for true accuracy and to really know what's going on. To suggest otherwise just misleads people that don't have a strong understanding of these issues.

Can one use a Lux meter for lamp positioning? Yes. Is it a good idea and a good option? No. I think it's irresponsible for people like you and I to suggest using a Lux meter is 'fine', even though a Lux meter can be used, we shouldn't promote it's use unless no other options are available.

Here is the spectral response of a Lux meter superimposed over the average quantum yield for higher green plants.

• This makes it obvious why a Lux meter (or footcandle, etc.) is a fail when one wants accuracy and true measure of 'what plants use'

​

And here's two more for people to get a better understanding of these issues.

• In the first screenshot below, it's figure C that we should use, on average.

​

FWIW,
After many months of testing with my quantum sensor I find these values are pretty much ideal:

• ~800-1,000 umol/area^2/second for veg, early-flowering and full-flowering (when daylength is > 10 hours; this has to due with Daily Light Integral, see this thread wherein I posted much info on the topic wrt cannabis, etc.)
• ~500 umol/area^2/second for seedlings (this produces VERY compact seedlings, no stretch and big leafs)
• ~100 umol/area^2/second for cloning

P.S.
Using a non-cosine corrected light sensor is another negative issue in terms of accuracy and true measurement of irradiance. We need to use cosine corrected light sensors for real accuracy.

 

[alkalien]

For making measurements concerning the differences between different Lamps and stuff like that you are right! We call that "quantitative" don't know how to translate that. On the other hand for comparing the lighting at different positions you can use any lightmeter you can get your hands on. The german word ist "qualitative".

So if you wanna know whether the light is distributed evenly throughout your growspace it is not important if the reading is normalised for the human eye or if it is just counting photons. The value will be "wrong" anywhere, but the twice the value does mean twice the light strength. That is, of course, assuming there is no frequencyshift due to reflectors and stuff.

So far, knna is right.

If you want to measure absolute values like the one you suggest, you can't use a lux-meter. That's where you are right! Great post though!

 

[spurr]

For making measurements concerning the differences between different Lamps and stuff like that you are right! We call that "quantitative" don't know how to translate that.

It's not translated, that's the English word, it's not a German word.

On the other hand for comparing the lighting at different positions you can use any lightmeter you can get your hands on. The german word ist "qualitative".

The word "qualitative" is English, not German. And I'm sorry but I disagree. Anytime you use a light meter it's quantitative (light 'strength', i.e., irradiance), not qualitative (light quality, i.e., spectrum).

You cannot use a Lux meter to accurately "[compare] the lighting at different positions" because those light meters do not 'measure' all photon in PAR range equally. The problem is one of spectrum, which changes with time, temp, input power, etc. And the spectrum strongly effects the quantitative measurements from a Lux meter, but not from a good quantum sensor. Thus, using a Lux meter will work, but it's far from ideal and it's far from accurate wrt how plants use photons in PAR range vs how human eyes use photons in PAR range.

A spectroradiometer is both qualitative and quantitative, but Lux meter, foot-candle meter and quantum sensor are only quantitative.

So if you wanna know whether the light is distributed evenly throughout your growspace it is not important if the reading is normalised for the human eye or if it is just counting photons. The value will be "wrong" anywhere, but the twice the value does mean twice the light strength. That is, of course, assuming there is no frequencyshift due to reflectors and stuff.

That last sentence is the problem with Lux and foot-candle meters, in fact, it's the crux of the problem. Because every lamp's spectral quality (re qualitative) is affected by that issue, as I noted above (i.e., age, temp, input power, etc.).

It's why we cannot use Lux or foot-candle meters to accurately place a lamp. Also, as I noted above, academic data wrt cannabis rate of photosynthesis (Pn) is in PPFD, not Lux. So cannabis growers have no 'gauge' as to where they should place their lamp using Lux, with the exception of the old study I found (re 100,000 Lux gave higher Pn than < 100,000 Lux).

So far, knna is right.

Again I disagree. However, I do agree that Lux can be used, but it's far from ideal, as I noted in my post above yours.

If you want to measure absolute values like the one you suggest, you can't use a lux-meter. That's where you are right! Great post though!

Thanks and ditto to you, well, with the exception of where we respectfully disagree with each other.

P.S.
IMO cannabis growers should get out of the mindset that Lux meters are okay, because they are not. They will work, but they're not okay in terms of being ideal or accurate.

 

[supermanlives]

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.

nope . i read and appreciate all his threads. he is smarter than the average bear.

 

[alkalien]

Thanks and ditto to you, well, with the exception of where we respectfully disagree with each other.

P.S.
IMO cannabis growers should get out of the mindset that Lux meters are okay, because they are not. They will work, but they're not okay in terms of being ideal or accurate.

I have nothing to add, it's like walking with crutches, can be done but far from perfect.
regards

 

[guest456mpy]

Hi spurr,

First off, I want to say that I understand everything you are saying and agree intellectually.

That being said, I would like to offer something for your consideration. Humans have marvelous pattern recognition and adaptive abilities. These abilities allow us to do complex things like driving cars, riding bicycles and flying planes without instrumentation. Using your reasoning I would need a range finder and accelerometer just to ride a bike (assuming we could balance without instrumentation.) But we don't, do we?

Quantifying variables exactly is paramount for scientific work, but it's not for practical use.

Humans can get "close enough" by interpolation of meter readings and plant behavior. This is really good enough for most growers.

Pragmatism over "mathurbation" in other words.

Just my $.02 worth, YMMV.

 

[spurr]

Hi spurr,

...

That being said, I would like to offer something for your consideration. Humans have marvelous pattern recognition and adaptive abilities. These abilities allow us to do complex things like driving cars, riding bicycles and flying planes without instrumentation. Using your reasoning I would need a range finder and accelerometer just to ride a bike (assuming we could balance without instrumentation.) But we don't, do we?

I'm sorry but that's a non sequitur. You're trying to compare apples and oranges. Let me try for a more apt comparison using your line of reasoning:

(Below the "bike" is our plants wrt growth, yield, and quality. "Riding the bike" and "cycling" is the act of growing cannabis. The "street" is ideal light quantity (irradiance) and "off the street" is non-ideal light quantity. The "d[FONT=Arial, Helvetica, sans-serif]owsing stick"[1] is a Lux meter and the "compass" is a good quantum sensor. This example is not meant to suggest you're an amateur grower, and I'm a professional grower, but for the purpose of this example such qualifications were needed.[/FONT])

-------------------------------------------------------
You wish to ride your bike on a street that was designed for bikes and well proven to provide the best bike riding experience, by far. Riding on the street allows you to get your full monies worth from your bike, e.g., what you spent to buy the bike, your helmet, riding shoes, time spent learning to ride, etc. However, if you veer off the street your bike responds less well; the wheels start to shake a bit, the breaks don't work as well, the seat starts to hurt you ass, and you get less overall benefit from the bike. In other words, you do not get your monies worth out of your bike, helmet, time spend riding, etc.

The only problem with this scenario is that the street is invisible, and you can't feel or smell the street. You cannot use your intuition to know the location of the street, and you cannot ask other cyclists such as yourself for the location of the street because they do not know its location. The only way to find the street is to use a compass, which costs more than a d[FONT=Arial, Helvetica, sans-serif]owsing[/FONT] stick commonly used by other amateur cycles, such as yourself, to find their way while riding off the street. However, the compass is used by professional cyclists so they can stay on the street and ride better than amateur cycles plodding along off the street.

You stop a professional cyclist and ask her how much her compass costs and the results of riding on the street vs off the street, she tells you and you scoff. You then try to compare your off the street bike riding experience to her on the street bike riding experience. And the professional cyclist tells you that you cannot compare the two because one is so much better than the other. That, and you cannot use your dowsing stick to even find the sidewalk next the street.
-------------------------------------------------------

Thus, with that more apt comparison between a quantum sensor (i.e., compass) and Lux meter (i.e., dowsing stick) wrt providing ideal and proven irradiance (i.e., riding on the street) for best cannabis growth, yield and ROI ("Return On Investment"), I think it's quite obvious why Lux meters are a fail for ideal growth and yield (i.e., biking riding experience).

In summation:

Can you use your dowsing stick for directions while riding your bike? Yes, most certainly. However, will you ever find the street with your dowsing stick? No. Not unless you have much dumb luck and wander onto the street. However, even if you mange to find the street by accident you cannot stay on the street for long because it's so easy to veer off the street, because the street is not straight and flat.

Quantifying variables exactly is paramount for scientific work, but it's not for practical use.

Why would you assume "practical use" and "scientific work" are are not one in the same? In other words, why would you assume "practical use" and "scientific work" are not mutually inclusive (you suggest they are mutually exclusive)? For you to assume so much demeans cannabis growers as a whole, IMO. Why should not cannabis growers use accurate measurement of light proven to provide best growth, health, yield and quality? (those are rhetorical questions, I'm not really looking for a response to them)

Humans can get "close enough" by interpolation of meter readings and plant behavior. This is really good enough for most growers.

Maybe for yourself, but please don't assume to speak for all cannabis growers. Some of us prefer to go beyond the mindset of: "fuck it, it's close enough, I'm too lazy/apathetic to care about getting it right and helping my plants be the best they can be".

Pragmatism over "mathurbation" in other words.

Just my $.02 worth, YMMV.

It's funny to me that you too use that term, considering there is zero math involved in using a quantum sensor. Its' just as easy to use a quantum sensor as a Lux meter ... and far, far, far more appropriate when growing plants such as cannabis.





[1]

 

[spurr]

Thanks and ditto to you, well, with the exception of where we respectfully disagree with each other.

P.S.
IMO cannabis growers should get out of the mindset that Lux meters are okay, because they are not. They will work, but they're not okay in terms of being ideal or accurate.

I have nothing to add, it's like walking with crutches, can be done but far from perfect.
regards

I agree 100% . And once a person is healthy enough (i.e., willing to spend the money) they will stop using crutches (i.e., Lux meter) and walk on their own two legs (i.e., quantum sensor).

 

[guest456mpy]

Quote:
Originally Posted by Hempyguy View Post
Hi spurr,

...

That being said, I would like to offer something for your consideration. Humans have marvelous pattern recognition and adaptive abilities. These abilities allow us to do complex things like driving cars, riding bicycles and flying planes without instrumentation. Using your reasoning I would need a range finder and accelerometer just to ride a bike (assuming we could balance without instrumentation.) But we don't, do we?
I'm sorry but that's a non sequitur. You're trying to compare apples and oranges. Let me try for a more apt comparison using your line of reasoning:

(Below the "bike" is our plants wrt growth, yield, and quality. "Riding the bike" and "cycling" is the act of growing cannabis. The "street" is ideal light quantity (irradiance) and "off the street" is non-ideal light quantity. The "dowsing stick"[1] is a Lux meter and the "compass" is a good quantum sensor. This example is not meant to suggest you're an amateur grower, and I'm a professional grower, but for the purpose of this example such qualifications were needed.)

-------------------------------------------------------
You wish to ride your bike on a street that was designed for bikes and well proven to provide the best bike riding experience, by far. Riding on the street allows you to get your full monies worth from your bike, e.g., what you spent to buy the bike, your helmet, riding shoes, time spent learning to ride, etc. However, if you veer off the street your bike responds less well; the wheels start to shake a bit, the breaks don't work as well, the seat starts to hurt you ass, and you get less overall benefit from the bike. In other words, you do not get your monies worth out of your bike, helmet, time spend riding, etc.

The only problem with this scenario is that the street is invisible, and you can't feel or smell the street. You cannot use your intuition to know the location of the street, and you cannot ask other cyclists such as yourself for the location of the street because they do not know its location. The only way to find the street is to use a compass, which costs more than a dowsing stick commonly used by other amateur cycles, such as yourself, to find their way while riding off the street. However, the compass is used by professional cyclists so they can stay on the street and ride better than amateur cycles plodding along off the street.

You stop a professional cyclist and ask her how much her compass costs and the results of riding on the street vs off the street, she tells you and you scoff. You then try to compare your off the street bike riding experience to her on the street bike riding experience. And the professional cyclist tells you that you cannot compare the two because one is so much better than the other. That, and you cannot use your dowsing stick to even find the sidewalk next the street.
-------------------------------------------------------

Thus, with that more apt comparison between a quantum sensor (i.e., compass) and Lux meter (i.e., dowsing stick) wrt providing ideal and proven irradiance (i.e., riding on the street) for best cannabis growth, yield and ROI ("Return On Investment"), I think it's quite obvious why Lux meters are a fail for ideal growth and yield (i.e., biking riding experience).

In summation:

Can you use your dowsing stick for directions while riding your bike? Yes, most certainly. However, will you ever find the street with your dowsing stick? No. Not unless you have much dumb luck and wander onto the street. However, even if you mange to find the street by accident you cannot stay on the street for long because it's so easy to veer off the street, because the street is not straight and flat.




Quote:
Originally Posted by Hempyguy View Post
Quantifying variables exactly is paramount for scientific work, but it's not for practical use.
Why would you assume "practical use" and "scientific work" are are not one in the same? In other words, why would you assume "practical use" and "scientific work" are not mutually inclusive (you suggest they are mutually exclusive)? For you to assume so much demeans cannabis growers as a whole, IMO. Why should not cannabis growers use accurate measurement of light proven to provide best growth, health, yield and quality? (those are rhetorical questions, I'm not really looking for a response to them)

Quote:
Originally Posted by Hempyguy View Post
Humans can get "close enough" by interpolation of meter readings and plant behavior. This is really good enough for most growers.
Maybe for yourself, but please don't assume to speak for all cannabis growers. Some of us prefer to go beyond the mindset of: "fuck it, it's close enough, I'm too lazy/apathetic to care about getting it right and helping my plants be the best they can be".

Quote:
Originally Posted by Hempyguy View Post
Pragmatism over "mathurbation" in other words.

Just my $.02 worth, YMMV.
It's funny to me that you too use that term, considering there is zero math involved in using a quantum sensor. Its' just as easy to use a quantum sensor as a Lux meter ... and far, far, far more appropriate when growing plants such as cannabis.

My dear spurr,

I don't want to argue with you, nor do I intend to change your mind.

However in future please keep in mind that most people have no interest in being absolutely accurate, just getting the job done. It must be awfully lonely in your ivory tower, so sad for you as the rest of humanity is doing just fine without playing scientist.

Hope someday your mind may actually be open enough to hear someone else's ideas without resorting to defend your own.

PS I'm a retired IEEE fellow who designed nuclear imaging for a very large German Engineering corporation. I have probably forgotten more than you'll ever learn, particularly with a closed minded attitude.

You won't have me bothering you since you already "know it all".