Should I get yellowing at 600w?

[GrowLightResearch]

So measurements extremely close to the light can also show a hint of "inverse square".

This is true.

because then the reflection isn't countering the effect yet.

This is false.

It's because of the five times rule. Do you understand why there is a five times rule?
What were the dimensions of the fixture?
For ISL to work well at 5", the fixture cannot be more than 1" corner to corner.
If you supply me with the size of the fixture, the number of and orientation of the LEDs I can calculate the results you measured.

This five times rule is the problem I was working on ≈18 months ago, August 18, 2016.
It was a small 12" strip with 16 LEDs measured from 200 mm down to 100 mm in 20 mm increments.
What I did was calculate ISL for each individual LED as 16 light sources and summed the16 intensities at each distance (height).

The results were nearly perfect given the setup required for accuracy with such small distances.
ISL worked perfectly for both measured and calculated values.

Point Source Approximation
The inverse square law can only be used in cases where the light source approximates a point source. A general rule of thumb to use for irradiance measurements is the “five times rule”: the distance to a light source should be greater than five times the largest dimension of the source. For a clear enveloped lamp, this may be the length of the filament. For a frosted light bulb, the diameter is the largest dimension. Figure 6.2 below shows the relationship between irradiance and the ratio of distance to source radius. Note that for a distance 10 times the source radius (5 times the diameter), the error from using the inverse square is exactly 1 %, hence the “five times” approximation.
-International Light Technologies, https://www.intl-lighttech.com/basic-light-measurement-principles-chapter-6-light-measurement-tutorial
https://www.intl-lighttech.com/basic-light-measurement-principles-chapter-6-light-measurement-tutorial​

Also, ISL is for isotropic approximate point light sources.
LEDs light distribution does not radiate the same intensity in all angles as a light bulb does.
Therefore the calculations must take the angle of the light light source with respect to the sensor and the distance of the light light source to the sensor.


At a height of 5" with a 48" strip with the sensor located below the center LED, the angle of LED to sensor and the last LED on the end of the strip is 78° and the distance 24.52".


At that angle and distance the ISL for the center LED with a 0° angle and distance of 5" only the center LED will follow ISL.


A Samsung 561C LED has a relative intensity of 17% at 78°.

By ISL, the intensity at 24.53" is 4.16% of the intensity at 5".

​

 

[wietefras]

It's because of the five times rule. Do you understand why there is a five times rule?
What were the dimensions of the fixture?
For ISL to work well at 5", the fixture cannot be more than 1" corner to corner.

Maybe now you understand why we keep telling you to use a full fixture for this test and why we keep telling you to use a "normal" distance from light to sensor/plants?

To test the actual situation which we grow in. That's where it's an inverse linear relation. While you desperately keep looking for theoretical situations where there is an inverse square relation.

Also good that you "researched" this "problem" that it's an inverse linear relation for us 18 months ago. However we don;t see it as a "problem" call it "reality". In fact it's because of the "solution" of reflective walls that we don't have an inverse square relation. So thanks, but no thanks.

 

[GrowLightResearch]

Just finally build yourself a full fixture and measure the light at 5", 10" and 20" in a properly reflective tent.

I am currently testing six BXEB-L0280Z-30E1000-C-B3 Gen2 strips in a 22 x 24 (4" between strips)
At 4" distance, with the tent closed up, the PPFD increases from 283 µMoles max to 292 , when the sides of the tent are removed.
Tent is Gorilla Lite 24" x 30".

No sides 283 µMoles
back only 282 µMoles
+ left side 293 µMoles
+ right side 282 µMoles
closed up 292 µMoles

293 to 282 is only 3%. I do not see that as significant reflective irradiance.
More likely the difference was caused by the instability of the currents becasue the strips are wired three pairs of strips in parallel. But that's another story.
HLG-240H-54A @ 1450mA x 3 2S 3P
Strip Temperature: 56°C.

No sides 247 µMoles
back only 249 µMoles
+ left side 250 µMoles
+ right side 251 µMoles
closed up 255 µMoles

So why only a 35 µMole difference from 4" to 8"?
Is it maybe as the height increased more LEDs could be seen by the sensor?
And at a lesser angle (i.e. increased intensity)?

Does not appear to be reflection related.
There are issues with the parallel wiring. I have ordered an HLG-

 

[wietefras]

So why only a 35µMole difference from 4" to 8"?
Is it maybe as the height increased more LEDs could be seen by the sensor?
And at a lesser angle (i.e. increased intensity)?

Does not appear to be reflection related.

Sure, keep sticking your head in the sand and deny reality.

Do you continuously hum "Must. Find. 'ISL' ... Must. Find. 'ISL' ..." while you are doing this "research"?

BTW It's reflection and overlap. Light comes more and more from strips around and fills in what is lost from the strip straight overhead. Reflection has the same effect as overlap.

Although in this case the error is caused by the tent walls not being rigid. Moving reflective foil will move light somewhere else.

In fact you shouldn't be doing a single measurement, but you should to measure average PPFD over the whole surface. That prevents/fixes all kinds of measuring errors.

 

[GrowLightResearch]

tent walls not being rigid.

Really? What tent has rigid walls? When closed up the sides are stretched skin tight.

Light comes more and more from strips around and fills in what is lost from the strip straight overhead. Reflection has the same effect as overlap.

My experiment was very conclusive that reflective film has very little effect. Like overlap?

When you describe this overlap term you fabricated, it describes ISL. "Overlap" is why ISL works.


You have provided nothing that backs your hypothesis on reflection and "overlap"?.
Overlap? I must have missed that day in physics class.

In fact you shouldn't be doing a single measurement, but you should to measure average PPFD over the whole surface. That prevents/fixes all kinds of measuring errors.

Although in this case the error is caused by the tent walls not being rigid.

Quit being a weasel.
Did you forget the measurements matched the calculations with only 1% error?

Sure, keep sticking your head in the sand and deny reality.

Show me something real! A hypothesis is just that. You need to back it up. You got nothing.
Overlap is not a real thing. You made that up. I striped the reflective film wall by wall. How can you deny that?

The five times rule is real. ISL works. Overlap is not a real thing. Reflective film is not an issue.

You did not address the five times rule. Is it a real thing in your mind? Why did not not mention it?

Moving reflective foil will move light somewhere else.

Reflectivity is a probability not a certainty. The issue is more Nobody understand reflectivity that well. How the photon reflects is not know that well.

You really should watch the video of the Nobel physicist explain photon reflectivity, transmissin, and refraction to a general public audience.

[/QUOTE]

 

[ANC]

If the wall isn't perfectly flat it may just have a nice fat bulge in the middle scattering light in all directions

 

[GrowLightResearch]

If the wall isn't perfectly flat it may just have a nice fat bulge in the middle scattering light in all directions

Yes there is scatter, called diffuse reflection, when the surface is not perfectly smooth. It is the aluminum coating protected by the mylar that reflects.

One problem is the one has a tendency to perceive a photon to act like a billiard ball bouncing off a rail. But it is a massless electromagnetic energy. It does not bounce off the reflective film like you may think. I was tempted to say a photon is smaller than an atom or electron. A photon is energy and has no known size. I'm even sure there is a scientific consensus on the photon. Whether a photon has mass has been a huge controversy. There is so little known about photons. We know they exist because we have devices (photo diodes, CCD, etc) that react when a photon .come in contact. This gives us the ability to experiment with photons. No one knows WHY they do the things they do. We know some of the things they do, not why.

Watch the video I previously mentioned. It's an older video and there may be more known now due to the recent research done in fiber optics. In fiber optics refraction takes reflectivity out of the equation. When driving on a dry dark road is completely different when it is raining, that is refraction from the water. As are the colors when oil floats on water.

It the charlatan vendors that sell reflective film are a big part of this misunderstanding. When they say a film is 90 some percent reflective means it is that reflective at one specific angle. It is not reflective over most incident angles of reflection (fairly confident on that). This image is from a patent on a device that measure reflectivity.

From: https://www.google.com.mx/patents/US20050286053

 

[ANC]

All I know is I need to cycle the plants against the white painted walls with the ones on the edges of my grow, or they grow faster on one side.

 

[wietefras]

Show me something real! A hypothesis is just that. You need to back it up. You got nothing.

I have YOUR OWN measurements demonstrating that it's not an inverse square relation. Also, there are dozens if not hundreds of people who created PPFD matrices of full fixtures. Not one shows an inverse square relation. Not even the ones without reflective walls

Overlap is not a real thing. You made that up. I striped the reflective film wall by wall. How can you deny that?

Overlap and reflection are real. The fact that you don't understand it doesn't make it less real. You understand nothing anyway so that's hardly a yardstick.

You won't see reflection at 4" under the light in the middle of a tent no, but you do already see overlap there. Hence no inverse square even that close to the lights like you already confirmed over and over.

Maybe you have less trouble looking at pictures: http://transitionbath.org/led-try-buy-scheme/led-light-intensity-from-different-beam-angles/

The light keeps spreading according to inverse square and at some point they start to overlap and light from neighboring light points fills in what is "lost". It just so happens that we hang our lights so that we do get this overlap because otherwise we would end up with hot spots and dark spots. So it's a perfectly normal thing to have overlap in a grow. Not a hypothesis, but actual reality.

Reflection keeps the light confined so it cannot spread out over a quadratic growing area. How on earth can you not understand this?

The five times rule is real.

Yes, and still amazingly you still do not get that when you do not NOT conform to that rule, inverse square does not apply. Why do you think that "five times rule" exists.

It's bizarre how cognitive dissonance keeps you from seeing the forest for the trees.

Heaps and heaps of evidence show that you are wrong. Yet you keep insisting that everybody is doing something wrong to get these figures which exactly match what a sane person would expect. You even pretend that you are doing something wrong yourself when you get measurements which confirm what everybody is trying to tell you.

Anyway, I'm done with this nonsense. You just either don't want to understand or are completely incapable of understanding these basic concepts. So if after this final attempt you still don't understand, I give up. Can't train a steer excrement to design grow lights I guess.

 

[GrowLightResearch]

I need to cycle the plants against the white painted walls

I like your reasoning. Great way to test reflective surfaces. Do the plants like it?
That's very interesting. Reflectivity off a white wall would be very different than a metalized film. The photons reflect off the aluminum coating on the back side of the mylar. Your white paint has pigments and a binder with different refraction indices which causes the refraction causes a difference in reflection. More refraction = more scatter. Scatter is reflected light just a different type than metalized film or mirrors. Just thinking out loud.

Did you use a specific white reflective paint like what is used on roofs? Is it matte or a sheen paint?

What's the height if the fixture over the canopy? LED?

 

[ANC]

Naah, just a coat of an ordinary matt finish low VOC paint.
If I had to guess, about 50cm.

 

[GrowLightResearch]

The fact that you don't understand.

How on earth can you not understand this?

amazingly you still do not get that

It's bizarre how cognitive dissonance keeps you from seeing the forest for the trees.

How about sticking to the facts? Oh that's right you have no facts.

quadratic growing area

"quadratic growing area" Really? Interesting choice of words. Not applicable here.

Heaps and heaps of evidence show that you are wrong.

You previously stated there is no evidence so you had no citations, it is just your common sense. Now there is heaps and heaps of evidence? Why do you not present any of it?
All you do is say I am wrong and your are right but you have nothing to back up what you say. You say others agree with me. You insinuate I never built a fixture, never grew anything. Very presumptuous. And incorrect.

Maybe you have less trouble looking at pictures

Yes, I like pictures. I know what the word overlap means. You brought overlap into the picture when your hypothesis on reflection canceling ISL started falling apart.

I found that grow lights did not follow ISL. I have been saying that is because a fixture must be looked at as multiple point sources and ISL must be calculated for each source of light. I tried that and it worked perfectly. I use ISL to do the calculations. You said it was all wrong and what I am doing will not work becasue reflection completely negates ISL. So I looked into what you said and found nothing that would support what you say. I ran experiments. A single CoB works exactly as ISL says. Reflection had no effect. I even found coated mylar does not do what the seller's claim.

I think it is a huge problem that growers do not know where to optimally position the fixture over the canopy. PPFD cannot be measured. PPFD must be calculated. I calculate the relative intensity for every square inch of the grow area. I calculate that intensity based on the distance to each square inch from each and every LED and the LED's spacial radiation pattern at the angle between every square inch and every LED.
Of course the light from the LEDs overlap. ISL still works. It just cannot be measured accurately due to the five times rule. Yet you insist 5x rule is not the reason. You give it a name, but do not say WHY. Is it reflection? Is it "overlap"?

With a reflective wall the light cannot spread any further than those walls and the inverse square stops once the light starts bouncing back off the wall.

So you said: "inverse square stops once the light starts bouncing back off the wall."
I showed you the measured results were unaffected by reflection. Reflection added 3% but had no effect on inverse square.
You say overlap. Yet offer nothing as to how overlap plays a part. Yes I agree with what you say about overlap. the problem is it has nothing to do with ISL.
Overlap exists but it works with ISL. That is what I found in my first set of data you said was wrong. My calculations correlate with the measured data. Yet you just say it is wrong. I take the time to experiment with what you claim and find you were wrong. Then you try to wriggle out of what you previously said.

So measurements extremely close to the light can also show a hint of "inverse square" because then the reflection isn't countering the effect yet.

No it is the opposite. Inverse square works better at greater distances. Reflection has zero effect on ISL.

you keep insisting that everybody is doing something wrong

All I have been saying all along is that YOU are wrong when you say reflection cancels inverse square. That's all. All you have been doing is slinging mud. You have no evidence to back you statements. Just because you think you understand but do not understand WHY things happen does not mean I am wrong. Not matter how many times you say it.

Yes, and still amazingly you still do not get that when you do not NOT conform to that rule, inverse square does not apply. Why do you think that "five times rule" exists.

 

[GrowLightResearch]

You won't see reflection at 4" under the light in the middle of a tent no

Reflection had zero affect on ISL at 36" and 40"
The measured values matched calculated ISL.

No Sides 40" 97 µMoles
No Sides 36" 117 µMoles

closed up 40" 127 µMoles
closed up 36" 154 µMoles



So reflection does not affect ISL at 4" or 1 meter. Got any new ideas? Your previous reflection hypothesis did not pan out.

Reflection has the same effect as overlap.

Was this a typo or did you really meant it? If so how are they related?

 

[nfhiggs]

No Sides 40" 97 µMoles
No Sides 36" 117 µMoles

closed up 40" 127 µMoles
closed up 36" 154 µMoles

You really consider a 30% increase with the sides closed up to be "zero effect"?

 

[GrowLightResearch]

You really consider a 30% increase with the sides closed up to be "zero effect"?

We are talking ISL. Apparently you did not notice the measured values closely match ISL calculations.

You may have missed the previous post where the reflectivity was only 3%.
I also said reflective film will work for HPS which are typically 1 meter above the canopy.
In the target LED fixture height range reflectivity adds only 3%.

I chose an unconventional setup that would emphasis the point reflectivity has zero effect on ISL.
If your LED fixture is 40" above the canopy you have bigger problems.

I am not going to position my fixture at 40" to get improved reflectivity at severe cost in intensity.

The objective is to position the grow lights as close to the canopy as possible and adjust the current (intensity) to the optimal level.

@wietefras has been saying reflectivity cancels ISL. It does not. Overlap is an ambiguous phenomena and I do not see how it is applicable. It's nearly the definition of ISL.

If you have anything to contribute to a solution that would be welcomed.
If there are any measurements you would like me to make and report, let me know.

What I am trying to do is provide an app that will locate the ideal height for the fixture. This is not a commercial endeavor. I'm not selling anything. Everything I do is open source.

The stumbling point is the inability to accurately measure irradiance.

I have already proven ISL works if you treat each LED as an individual point source. And when I say point source it is meant as an approximate point source within the 5x rule. Although I am very pleased the latest measurements show a 2X measurement is not that bad. But I purposely used a small fixture (22" x 24").

I am very close to a solution. A little help would be more productive than negativity.

 

[Jimmy the vest uk]

I like your reasoning. Great way to test reflective surfaces. Do the plants like it?
That's very interesting. Reflectivity off a white wall would be very different than a metalized film. The photons reflect off the aluminum coating on the back side of the mylar. Your white paint has pigments and a binder with different refraction indices which causes the refraction causes a difference in reflection. More refraction = more scatter. Scatter is reflected light just a different type than metalized film or mirrors. Just thinking out loud.

Did you use a specific white reflective paint like what is used on roofs? Is it matte or a sheen paint?

What's the height if the fixture over the canopy? LED?

Yeah Matt white paint is better than gloss white for reflectivity apparently I am not a scientist and have no idea why this is I’m sure you can explain, try use short words and small sentences I been smoking a lot of weed at all times

 

[nfhiggs]

A little help would be more productive than negativity.

Not being negative. Just curious why you equated a 30% increase in light levels at 36 and 40 inches with "zero effect". Clearly there IS an effect. Whether it effects your calculated ISL ratios is not really the point - the point is that light levels increased by 30% (at that level) simply by closing the tent in. I'd be curious to see the differences at 4" intervals between the 8" and the 36" distances.

And while I also do not intend to raise my lights 40" from the canopy, having increased light levels at various depths below the canopy, regardless of how its getting there, is certainly beneficial to yield.

Flat white paint has long been considered the optimum BTW.

 

[wietefras]

@GrowLightResearch So you still don't understand. Who would who have thought it. Oh wait I did.

Just one last tip though. Try actually doubling the distance and see if the intensity drops by 4. Don't take two measurements at almost exactly the same height. You are suffering from measuring errors, an incredibly crappy grow tent and confirmation bias so much that you really need to cover for that.

Like I said, try 4", 8" and 16".

@nfhiggs
It depends on what you consider optimum. Flat white paint is not the optimum for maximum reflection towards the plants, but it does add some diffusion. If you have a harsh light source, flat white can be beneficial. For instance in green houses it makes sense to use flat white paint since there is too much sunlight anyway and the harsh direct light of the sun can benefit greatly from adding some diffusion.

For led lights this is not the case. It's diffuse enough already. Fully diffuse reflective surfaces will bounce half of the reflected light back away from the plants. That's not helping.

There are plenty tests on youtube showing that there can be big differences in light going to the plants depending on what reflective material is used on the walls.

For instance someone simply trying some mylar in his flat white painted room:

This guy tests a few materials:

With an explanation why overly diffuse reflection isn't better in our case:

 

[GrowLightResearch]

Not being negative.

I appreciate that. I will try to do better in that department too.

Just curious why you equated a 30% increase in light levels at 36 and 40 inches with "zero effect".

When I said that I had not done those measurements. I may regret that statement and may have been wrong. My hypothesis on that matter is this: Those measurements were taken in a small tent with no canopy to absorb much of the light before it was reflected. The strong rays of photons are generally directed at the canopy and it is the weak rays (due to incident angles) that reach the walls. I was surprised at the 30%. I still published them even though they contradicted what I had said because it was the right thing to do.

Not saying that to defend what I said. The truth is, I no longer know if it is true or not. For now I will recant my statement on the zero effect of reflections affecting irradiannce. I do NOT recant my statements on ISL and reflectivity. I do not understand reflection and the more I look into I am finding more about how little is known. I was able to prove reflections do not affect ISL.

I do have the measurements posted above in this post at 40”, 36”, 8”, and 4”. It's a bit time consuming and a real pain in the ass to zip and unzip the tent sides.

The first ones I did yesterday were were at closer distances. Later yesterday I did the measurements at 40” and 36” because I figured those would show better results for reflectivity but were not real life. There are many factors and reflectivity is extremely complex. What works for one may not work for another. After watching the youtube reflectivity lecture by the Nobel physicist (referenced in this thread) I no longer have any hope of ever understanding photon reflections. Not that the lecture was that difficult to understand he made if very clear it is a mystery why photons reflect. Reflection is NOTHING like a billard ball bouncing off the rail. Essentially that is the way it “appears” to work but it's not. Snells Law leaves out the complexities and it is still difficult to understand.

Most of my recent research into reflectivity has been with coated mylar. When @ANC mentioned his plants lean toward the white painted wall that got me thinking in a different direction. I did a little research on paint and it is a whole different story compared to metalized mylar. I also found an easy to understand paper written by a paint guy (engineer? scientist?).

The only reason I was able to do those measurements is I was working on a project and everything needed was already setup. If I find some time I will make those measurements for you.

One thing I have been seeing about reflectivity that kind of pissed me off. When a product specifies reflectivity does not mean it will have the same reflectivity and any angle. I have been seeing a lot of graphs for various materials showing the reflectivity drops off rather quickly when the angle changes. Many times at only 30° off the angle used to specify the reflectivity there is zero reflection. I do not have all the details on that but some day soon I will. Now I am very skeptical when I see videos like were post here. There many times more to the story than meets the eye. Some people will deceive on purpose and others will believe it and repeat to others. Me I need to understand why. I'm not there yet with reflectivity. Not sure I have enough year left on this planet to get to that point.

If we could get 30% increase in real life that would be fantastic. That 30% motivated me to try and find out. 30% is huge but all I have seen so far in real life is dismal. I need to know more.

 

[wietefras]

Most of my recent research

Pffft. But god forbid someone calls you out for pretending to be a researcher.

Seriously, though don't appease this guy pretending he's engaging in a real discussion. Come on, his "research" invariably shows nonsense. Don't act like he's on to something, because then he most certainly will never learn and keep polluting this forum with his nonsense.