Light Penetration - misunderstood

[foaf]

What do people really mean when they discuss this? Do you buy into the common terminology? I personally think that the term is deceiving as it suggests that light coming from one type of source "acts" differently than light coming from other types of sources.

So I read all the time people saying "you need to this and that because LED lights/CFL light don't have as much penetration"

It's as if people think that somehow light from one source obeys different laws of physics than the light from other sources.

I have background in light measurements and analysis and have a patent on a special medical lighting systems fwiw, so Ive thought about all this a lot in different context anyway....and that term is annoying to me. Well, I'm easy to annoy anyway.

A common measurement of light is the "lux". Its not perfect for growing because it measures light as if it was the human eye, but the most common meters measure lux. PAR is better, but the meters are less common. LUX/PAR/ect. Lux takes into account the area covered, so it measures what actually hits the plant surface. For example (making up the numbers), a 1000watter that is 4 feet above the canopy might have the same lux as a 400watter that is 2 feet above the canopy, measured at a certain point.

Regardless of the light type or total ligth intensity, if the lux/par is similiar at one point in the canopy, then the lux 8 inches below the canopy is the similiar, so the "penatration" is the same.

The point is, this concept of penetration is a false concept except that more light is better both at the canopy and deeper into the canopy and more light at the canopy means more light deeper in the plant. If a bank of cfl lights or leds has the same lux/par at one part of the canopy as say a 1000 HPS, (of course the led/cfls might need to be closer to accomplish this), then the light levels deep in the plant would be the same too.

 

[blazesck]

A lot of people seem to think their HPS and MH lights are magical marijuana producers and everything else is garbage because they've never taken the time to try anything else. I also see lots of posts on this site where people would rather do nothing but try to find flaws in grows or reasons they're going to fail. I think it's more about post-count and ego than science or actually growing better buds.

 

[etinarcadiaego]

Well no, not all light behaves the same all the time, and yes one source can have more intensity than another . . .

May I ask what exactly your background is in this field? I only ask because your measurements are in units related to grow-lamp specs, rather than photonic measurement . . .

What you're referring to is part of quantum mechanics, you may want to look into the wave-particle duality.http://www.physicsforums.com/showthread.php?t=12539

 

[foaf]

Of course one source can have more intensity than another, and of course there are spectral differences. but... when someone says that light from x type of bulb has better penetration than light from y type of bulb, it is not a helpful statement. "Penetration" is possibly defined as the amount of light that hits the plant surfaces deep to the canopy. And it is a function of the amount of light at the top of the canopy and the density of the plants foliage. It is not dependent on the specific type of source bulb. Thats the point I was making while stoned this morning and having a semi insightful moment.

Intensity has two common measure, as related to light sources.

The total amount of light that is produced, this is good for determining the efficiency of a bulb.

The amount of light that strikes on any surface area of an object, PAR or LUX. This measure doesn't care if the light is from the sun or from a flashlight, it just measures the total amount of light that hits a small area at some location.

I did minor in physics, and I cant imagine that quantum mechanical considerations are a helpful component of measuring macroscopic light volumes. I took quantum mechanics, but in the early 80's that amounted to an entire semester dissecting the bohr equation, I suspect that its a different course now.

 

[diamondmine]

So... Will 1000watts of HID penetrate the same as 1000watts of cfl?

Let me rephrase that. Will 1000 lumens of HID penetrate the same as 1000 lumens of cfl? It does right?

 

[MaynardG_Krebs]

So... Will 1000watts of HID penetrate the same as 1000watts of cfl?

Let me rephrase that. Will 1000 lumens of HID penetrate the same as 1000 lumens of cfl? It does right?

Maybe.. depends..

mgk

 

[AcroPhobic]

A lot of people seem to think their HPS and MH lights are magical marijuana producers and everything else is garbage because they've never taken the time to try anything else. I also see lots of posts on this site where people would rather do nothing but try to find flaws in grows or reasons they're going to fail. I think it's more about post-count and ego than science or actually growing better buds.

I hear ya, you'll always have know it alls everywhere you go who think they are a master gardener/botonist trying to feed you bullshit. I've been growing for years and years but I dont claim to be a mariuana expert. I still have lots to learn. For the most part growing marijuana is as easy as growing a tomato plant and I grow 6 different tomato varietys every year along with 5 different peppers. Its not really some insane science, its a weed that doesnt need OUR attention to survive and produce, but WE as growers pamper our GIRLS. I do it because I take great pride and pleasure in growing MY own medication and want the BEST smoke I can possibly produce.

I see it as the same as myspace/facebook .. the more friends you have, the cooler you are? If that makes sense. Post counts and rep mean nothing to me. The knowledge found here does though.

 

[Weezard]

Pearl time.

Pearl time.

So... Will 1000watts of HID penetrate the same as 1000watts of cfl?

Let me rephrase that. Will 1000 lumens of HID penetrate the same as 1000 lumens of cfl? It does right?

No,
It will not.
In this case, it's about distance and the inverse square law.
If an HPS source is kept 12" above the top of a plant and that plant is 12" tall. the light at the bottom will have approximately 1/4 the intensity of the light at the top.

That is fact.

If your cfls/leds allow you to keep them 6" from the top of the plant. and that plant is 12" tall, the intensity at it's base will be approximately 1/9th of the intensity at the top! (Edit for my bad math)
It will be 1/4 at the middle of the plant.

(Subject to spectral absorbtion of the most useable wavelength by upper foilage, of course, but that is remedied by moving the light, or the plant to shift shadows.)


In sunlight. the intensity will be approximately the same, top and bottom.
In fact, to drop the intensity down to 1/4, at it's base, your plant would need to be approximately 93,000,000 miles tall.

That, is penetration to me.
So.
I use sunlight whenever possible.

When not possible, I use enough led light, to keep my girls 18" below the light when the top are getting all the light they can take.
That gives them the same math kine "penetration" as any other indoor light source .


Bottom line?
Light distance affects penetration in a measurable and repeatable way.

You no think so?
Whip out yer meter and waste yer time.
We'll wait.

All that said.
There is a simple "workaround" with LED emitters.

My meters tell me that very little is gained by growing in an enclosed space with reflective walls.
Li'l better, but only a few percent.
Yeah, I know, surprised me too, but da meter no lie.

However lensing the LED to a narrow focus.
(Or anything better than 180 degrees actually.)
Allows me to increase the distance between the light source and the tops while still keeping the maximum useful intensity at the tops. (About 91k LUX)


Aloha,
Weezard

 

[foaf]

Weezard, your thoughts about the inverse square law are something I had not considered. Thanks that is certainly an important thought, however, the inverse square law is only for a point source. In your proposed thought experiment, and I agree with it to some degree, the 1000 watts of cfl are actually spread out very much more than a point, whereas the HID light that is higher is more like a point. If you have a broad area of light, as you would have with an array of cfl or leds, the inverse square law doesn't apply as one would expect. I do agree it is a factor and one I hadn't considered.

add- I wonder if there may actually be the opposite effect sometimes depending on the setup. Consider that a source that is an infinite plane would have no decrease with distance. Of course even a broad panel of leds or cfls isn't infinite, but it may approximate it for some region of the grow. Also, perhaps since light comes from many angles, penetration may be better since it can get around blocking leafs from different angles. There is more to this than others or myself had considered I do think.

 

[Weezard]

It's the law.

It's the law.

Aloha Foaf

Weezard, your thoughts about the inverse square law are something I had not considered. Thanks that is certainly an important thought, however, the inverse square law is only for a point source.

In a perfect world.

But, I'm talking practice, not theory.

Since there is no perfect world, I investigate.
I have plenty for thinkin', but there comes a time when one needs proof.
(It's not about what I wish it to be, it's about what is.)
So, I set out, to find out, what is.
Observed, measured, and recorded from several light sources and types.

15" X 15" LED arrays, single point emitters, long tube fluorescents, cfls, sunlight, white walls, reflectix walls, mylar tents, etc.

Here are some results from arrays w/mylar:

Lambertian spread, roughly 160 degrees



~12K LUX



~ 3k LUX
Then, an array w/with lenses;





Hmmm. More like a 1/3rd than a 1/4th.

In your proposed thought experiment, and I agree with it to some degree,

Not a just a"thought experiment", it's "hands on"

Though, thinking is where everything starts.

When unsure, I always experiment.
I do enjoy the piddlin' aroun' as much as the knowledge gained.


the 1000 watts of cfl are actually spread out very much more than a point, whereas the HID light that is higher is more like an hid. If you have a broad area of light, as you would have with an array of cfl or leds, the inverse square law doesnt apply as one would expect.

Actually, a minor difference. It just takes the curve out of the measuring plane.
With the square footage we are concerned with, the measuring error is not significant.

I do agree it is a factor and one I hadnt considered.

Looks like the ISL still stands.
(Good thing too, science would be lost without it.)

You, I like.
Your brain works.

Aloha,

Weezard

 

[diamondmine]

Weezard- but wouldn't 1000 lumens of HID also be placed 6" from lightsource?
Seems to me the only reason a cfl is not as powerful as HID is because in order for cfl's to have the equal power as hid there has to be a lot of cfl's and that many cfl would take up much more area than hid.

 

[Weezard]

A twofer.

A twofer.

Weezard- but wouldn't 1000 lumens of HID also be placed 6" from lightsource?
Seems to me the only reason a cfl is not as powerful as HID is because in order for cfl's to have the equal power as hid there has to be a lot of cfl's and that many cfl would take up much more area than hid.

Rutro!
Yet more thinking to be done.
Hang on a sec. whilst I address dat last addendum.

"add- I wonder if there may actually be the opposite effect sometimes depending on the setup. Consider that a source that is an infinite plane would have no decrease with distance."

That is an interesting thought.
Of course, with vast distances there's gonna be spectral drift.
And attrition.
Space is not really a vacuum.

But, without the "spread" from the source, you make a fun point. ;-}
Whee! I love dis kine sing..

Of course even a broad panel of leds or cfls isn't infinite, but it may approximate it for some region of the grow. Also, perhaps since light comes from many angles, penetration may be better since it can get around blocking leafs from different angles.

Absolutely.
Mounted my first LED array on a "baby swing" to shift shadows.

There is more to this than others or myself had considered I do think.

Always is, my braddah!
Alo Ha again
__________________

Sorry 'bout dat D.M. editor got all uffy on me.
Where were we?
Oh, yeah!
"Weezard- but wouldn't 1000 lumens of HID also be placed 6" from lightsource?

Actually, no.
There's a top limit to the intensity that a plant can tolerate.
Differs with strain, but at 91k LUX most plants stop growing.
The leaf will thicken here in da tropics as plants protect themselves from too much light.
There's a mechanism called thylakoids that will stack together, edge-on to the light which makes the leaves visibly thicker. All that "sunblocking" takes energy so growth slows.
Above 91k LUX, light bleaching begins.
The leaf turns paper white
I dunno if the chlorophyl gets destroyed, or resorbed, but those leaves never recover.

That's why I overkill on my leds.
I exceed 91k LUX at about 6". That lets my raise the light up off the canopy to about 12" - 18" which increases effective penetration enough to grow decent 2.5" - 3' bloomer girls.

That is why most 1W. emitter based led arrays are only good for scrog and small areas.
It's not about lumens per Watt., it's about the power to penetrate.

So, now ya know my secret.
Enjoy!

Oh, and not fo' nuttin' but 1Kw. of CFLs whould be , um, un-weildy.
While they are quite efficient, unfortunately, theres an upper limit to just how many photons one can get from phosphors.

Thanks for the soapbox, brah.

You can post within my post anytime.

Weeze

 

[ericcalif]

No,
It will not.
In this case, it's about distance and the inverse square law.
If an HPS source is kept 12" above the top of a plant and that plant is 12" tall. the light at the bottom will have approximately 1/4 the intensity of the light at the top.

That is fact.

If your cfls/leds allow you to keep them 6" from the top of the plant. and that plant is 12" tall, the intensity at it's base will be approximately 1/16th of the intensity at the top!
It will be 1/4 at the middle of the plant.

I had to re-read this to make sure I understood. At first I thought you had your math wrong, but then I got what you were saying.
But I still see a flaw... Doesn't that obscure the outcome if you mix ratios like that?
HPS ---> top of canopy = 12" = 1/2 intensity.
top of canopy ---> bottom = 12" = 1/2 again intensity.
HPS ---> bottom of 12" plant = 1/2 of 1/2 = 1/4

24" from HPS = 1/4 intensity. ok. Inverse square.

So all things being equal, if in the second scenario we measure down 18", how do we wind up with 1/16 intensity? By changing the ratio of light source to canopy and canopy to bottom like you did.

All things being equal, 2 equally bright light sources, one measured 24" down, the other measuring 18" down, the latter would be more intense.
I think that's where the OP was coming from.

If you did the same scenario, one HPS 6" from the tops, the other CFL 6" from the tops, same intensity at the source, you would pretty much have the same intensity 18" away. Or 24" away. Not taking into account all the variables of lamp shape, reflectors, vegetation density, etc.

 

[Weezard]

Pretty much.

Pretty much.

"If you did the same scenario, one HPS 6" from the tops, the other CFL 6" from the tops, same intensity at the source, you would pretty much have the same intensity 18" away. Or 24" away. Not taking into account all the variables of lamp shape, reflectors, vegetation density, etc. "

Basically, you are correct, if, for intensity, you substitute "change of intensity".
(The intensity would only be the same if they were the same intensity at the start.)
However they will lose intensity at the same rate.
Because;


I'm just saying that the initial distance from whatever light source will be a determining factor in the effective penetration of that source.
Or.
The distance from your light source, at maximum light level, to your canopy, will determine, for the most part, how tall a plant one can flower successfully with that source.

I grow large plants indoors, under leds, (at least I used to when I had to), and I have just shared the reason I can do this with 5 - 15Watt emitters, when 1 Watt emitters simply can not.

For anyone itching for a great debate.
This is not a debate, it's a take it or leave it.
Got different facts? State 'em.

Aloha, Y'all
Weezard

 

[ericcalif]

View attachment 55430 [/FONT]


For anyone itching for a great debate.
This is not a debate, it's a take it or leave it.
Got different facts? State 'em.

Aloha, Y'all
Weezard

Good pic, that's what I was saying. (guess that's why a pic is worth a thousand words) No debate really, sounds like we're on the same, er, wavelength. Light is light, as far as 'penetration'.

 

[Ludo]

very nice thoughts you are thinking up here....! And thank you for clearing a few issues for me, and keep the good info comming, somehow it's more manageble for me to read it here then on another website......

 

[love?]

I'm hardly an expert on the subject but IMO the spectrum of the light has to affect the permeability because surely this is something where wavelength matters?

 

[Weezard]

Good pic, that's what I was saying. (guess that's why a pic is worth a thousand words) No debate really, sounds like we're on the same, er, wavelength. Light is light, as far as 'penetration'.

You were spot on, brah.

"So all things being equal, if in the second scenario we measure down 18", how do we wind up with 1/16 intensity? By changing the ratio of light source to canopy and canopy to bottom like you did."


Quite frankly, I was wrong.:
(I went back and corrected it on 5/5)
I think I was trying to take a 1/4 of a 1/4.
Really not a math kine guy,
That's why I have to actually try everything.
Sorry to confuse.
Good that it didn't obscure the point, though.
I think it's an important concept.



Da weeze

 

[Weezard]

Um, wait, what?

Um, wait, what?

I'm hardly an expert on the subject but IMO the spectrum of the light has to affect the permeability because surely this is something where wavelength matters?

Aloha.

I'm not really sure what you are saying here, brah.

I thought permeability referred to the speed at which a water penetrates a given substrate.

Anyroad,
wavelength matters for many things it's true.
It's long in red, and short in blue
However, one instance where it makes no difference at all, is the venerable Inverse Square Law.

The ISL applies from gamma rays on down, and from audio on up.

Plays no favorites.


Is that what you meant to ask?


Weezard

 

[guest456mpy]

If you did the same scenario, one HPS 6" from the tops, the other CFL 6" from the tops, same intensity at the source, you would pretty much have the same intensity 18" away. Or 24" away. Not taking into account all the variables of lamp shape, reflectors, vegetation density, etc. "

Basically, you are correct, if, for intensity, you substitute "change of intensity".
(The intensity would only be the same if they were the same intensity at the start.)
However they will lose intensity at the same rate.
Because of ISL.
I'm just saying that the initial distance from whatever light source will be a determining factor in the effective penetration of that source.
Or.
The distance from your light source, at maximum light level, to your canopy, will determine, for the most part, how tall a plant one can flower successfully with that source.

I grow large plants indoors, under leds, (at least I used to when I had to), and I have just shared the reason I can do this with 5 - 15Watt emitters, when 1 Watt emitters simply can not.

For anyone itching for a great debate.
This is not a debate, it's a take it or leave it.
Got different facts? State 'em.

This exactly what I've been trying get across to LEDGirl, but she stubbornly reuses to admit this. She advertises that her light are the world's most advanced LED systems, when in fact they are not!

I have also built DIY'd 5 watt emitter component based LED light with the same results.