Ichthyoid (Bill)-Riddle me this LED question please!

[acroholic]

I can't think of anyone more qualified to answer this than you, but if anyone else knows please feel free to post. I had someone ask me this via PM on another forum and I told them I'd try to find the answer.

Let's say you are running LEDs, and they are all the same, and are dimmable percentage wise. You have three units running, and you want to add a 4th. How do you keep the intensity level (PAR I guess) the same as 3 units after you add a 4th? Example, you run the 3 at 100%, a 4th unit adds 1/3 more total light, so do you dim the now 4 units by 1/3 down to 66% from 100%? Or is there more to it than this? I know with more units over a given tank space there will be more light overlap, etc.

Or is this basically a get a PAR meter and measure points on the reef and set your intensity level accordingly?

 

[dakota9]

I know this isn't directed toward me, but I want to ask in regards to the analogy above ;


Why would you add a 4th fixture if you want the same light as the original 3 fixtures provide?

 

[acroholic]

Dakota9;702845 wrote: I know this isn't directed toward me, but I want to ask in regards to the analogy above ;


Why would you add a 4th fixture if you want the same light as the original 3 fixtures provide?

An extra fixture would allow the user to run the LEDs at a lower wattage rating, I guess, which I believe would extend the life of the units. I didn't ask why myself. But this answer could apply to me as well since I just took down a tank that had three AIs on it. If I can't trade mine for some Sol Whites, they may end up on my 300.

 

[seth the wine guy]

FWIW Dave. When I added a third unit to my tank there was not a difference in the PAR measurements I took before and after. What did change was the radius of the consistent PAR results. Less "dead" or low PAR spots. Think of it as a partly cloudy day versus not a cloud in the sky. I had no expertise in this like Bill but it's my observation. (And analogy of course.) Feel free to dismiss me!

 

[ripped tide]

Following... I have some related questions about PAR. Can I post here or would you prefer I start my own thread?

 

[acroholic]

Seth The Wine Guy;702854 wrote: FWIW Dave. When I added a third unit to my tank there was not a difference in the PAR measurements I took before and after. What did change was the radius of the consistent PAR results. Less "dead" or low PAR spots. Think of it as a partly cloudy day versus not a cloud in the sky. I had no expertise in this like Bill but it's my observation. (And analogy of course.) Feel free to dismiss me!

That may be the answer.

Edit:

Ripped Tide;702860 wrote: Following... I have some related questions about PAR. Can I post here or would you prefer I start my own thread?

Post away. We can all learn something.

 

[ripped tide]

Thanks Dave. This may be a silly question, but what exactly does PAR stand for?

We use a quantum meter to take a measurement of the PAR, how do those work(this may be answered within the first question)?

All I have been told about PAR is that it is te "usable" light, so how do we determine what is usable and what is not?

Hypothetically, If I have 2 LED's that(individually) produce a PAR of 300 at 24", and I aim them at one central focus point at 24", will I get 600 PAR or 300, or other?

Light molecules are emitted as photons. Does the amount of photons effect the PAR or would it be the frequency, wavelength and distance that the light has to travel that effects the par?

I have more questions, but lets see how these go first.

 

[thanh386]

Photosynthetically active radiation

 

[ichthyoid]

Acroholic;702842 wrote: I can't think of anyone more qualified to answer this than you, but if anyone else knows please feel free to post. I had someone ask me this via PM on another forum and I told them I'd try to find the answer.

Let's say you are running LEDs, and they are all the same, and are dimmable percentage wise. You have three units running, and you want to add a 4th. How do you keep the intensity level (PAR I guess) the same as 3 units after you add a 4th? Example, you run the 3 at 100%, a 4th unit adds 1/3 more total light, so do you dim the now 4 units by 1/3 down to 66% from 100%? Or is there more to it than this? I know with more units over a given tank space there will be more light overlap, etc.

Or is this basically a get a PAR meter and measure points on the reef and set your intensity level accordingly?

Dave,

Thanks for the compliment/confidence, anmd for asking. This brings up some interesting discussion, I believe.

Actually this isn't too difficult of a problem, if we stop to think about what we are trying to determine. You may rememeber ratios and proportions from algebra (boooo, hisss from the crowd). Well this is a proportion. It goes something like this-

We know that we have 3 fixtures and they equal 100% of whatever light/PAR we get. We would like to duplicate that using 4 fixtures, so we write it like this-

100% is to 3 as, x is to 4 (x% is what we are tring to figure out), or

100 (3) = x (4) then multiply both sides by 1/4, and we get

100 (3)/4 = x or

300/4 = x so

75 % = x Run all 4 fixtures at 75% and you will get the same as 3 at 100%

Seth The Wine Guy;702854 wrote: FWIW Dave. When I added a third unit to my tank there was not a difference in the PAR measurements I took before and after. What did change was the radius of the consistent PAR results. Less "dead" or low PAR spots. Think of it as a partly cloudy day versus not a cloud in the sky. I had no expertise in this like Bill but it's my observation. (And analogy of course.) Feel free to dismiss me!

Seth, you are right on the money. This is known in both math and photo optics as integration (making everything the same). You determined through observation what I saw some college physics students never understand. (good job)

This is also the very reason everyone plays 'the optics shuffle' trying to get the beams from their LED's to overlap just so, so that the light/PAR ia all very uniform.

BTW- I have a solution for this, and I WILL be trying it at home

 

[ichthyoid]

Ripped Tide;702886 wrote: Thanks Dave. This may be a silly question, but what exactly does PAR stand for?

We use a quantum meter to take a measurement of the PAR, how do those work(this may be answered within the first question)?

All I have been told about PAR is that it is te "usable" light, so how do we determine what is usable and what is not?

Hypothetically, If I have 2 LED's that(individually) produce a PAR of 300 at 24", and I aim them at one central focus point at 24", will I get 600 PAR or 300, or other?

Light molecules are emitted as photons. Does the amount of photons effect the PAR or would it be the frequency, wavelength and distance that the light has to travel that effects the par?

I have more questions, but lets see how these go first.

First, PAR meters work on what is called the photoelectric effect. The sensor converts photons into electrical current, which is amplified and measured by the meter. Using a calibrated sensor+meter yields accurate results. FWIW- Albert Einstein actually won the Nobel prize for his work on the photoelectric effect, not on the Theory of Relativity.

PAR is based on a 'curve' of how well plants absorb photons. Different wavelengths (colors) are absorbed more or less efficiently, and that is factored in to generate the 'calibration curve' by the manufacturer.

Next, if you point two identical light sources at the same point, from the same distance, you will get 2x's the light/PAR.

It is also important to know that point source light behaves according to what is known as 'the inverse square law'. What does that mean? If you measure the intensity (actually called irradiance) at some distance, you will get 1/4th that intensity if you double the distance, and 1/9th if you triple the distance. Confused?

Technically speaking, PAR is based on the international standard unit of photons called...the einstein! 1 PAR = 1 microeinstein
What is an einstein? Well it is 6.02 x 10^23 photons (a really ginormous #)
This is also known as a mole to the chemists out there.

In practice the wavelength and distance do affect the PAR for reasons I have already mentioned. BTW- frequency and wavelength are just the inverse of one another.

Hope this helps.

 

[ripped tide]

Thanks Bill. I will be at the meeting tomorrow and I intend to find you and pick your brain further. This is all good stuff.

 

[ichthyoid]

also FWIW-

Photons are just REALLY high energy electrons.

This makes sense if your have ever used a dimmer connected to a clear incandescent light bulb. As you turn up the current to bulb using the dimmer, the coil inside the bulb begins to glow from the electron flow and resistance of the wire. Keep turning up the current and it gets brighter and brighter. This is due to photons being discharged from the wire. Where did they come from?

How 'bout them apples?

 

[ichthyoid]

http://t3.gstatic.com/images?q=tbn:ANd9GcTSj-bdIeFOKFQR3IMkTf77oy4JhKR7Uny0QuCqQ6KuYQphN2C9" alt="" />

Edit: [QUOTE=][B]Ripped Tide;702910 wrote:[/B] Thanks Bill. I will be at the meeting tomorrow and I intend to find you and[B] pick your brain[/B] further. This is all good stuff.[/QUOTE]

You do and you'll have to clean it up! :lol2:

 

[ripped tide]

ichthyoid;702901 wrote: First, PAR meters work on what is called the photoelectric effect. The sensor converts photons into electrical current, which is amplified and measured by the meter. Using a calibrated sensor+meter yields accurate results. FWIW- Albert Einstein actually won the Nobel prize for his work on the photoelectric effect, not on the Theory of Relativity.

My head is hurting too! Its all coming to me but hard to put into words what i want to say. I'm trying to follow, and correct me if I am wrong.

A photon is a high energy electron created by radiation. In most cases, electricity is the source of energy to produce photons. As the electrical current passes through the medium used, the particles begin to rapidly speed up and begin to radiate and exchange electrons. At what point do they convert to photons and begin to emit light?

A quantum meter converts the photon into electricity. Is this similar to how solar energy is produced?

During a normal electrical current, is there still significant electron exchange? Wouldn't this cause the particles to decay over time? How could the rate of decay be determined? And if there is no decay, there has to be some molecular change, right?

And if there is significant decay, would the cheap hardware used to make LEDs wear out before the diode itself?

Dave, I don't mean to jack your thread.

 

[acroholic]

Ripped Tide;702945 wrote: Dave, I don't mean to jack your thread.

No problem at all.

Bill, thanks for the explantation. That makes sense. It will do me as well if I end up adding my 3 AIs to the tank. I may just use them for blue accent, but If I incorporate them into the regular light schedule I know what to set them all at now, since my # of units is a multiple of the scenario I gave in the first post, it would be the same ratio.

 

[morganatlanta]

Is your 75% measuring LED output or current into the LED? The output curve vs. current is non-linear, so if it is current you are measuring, you have to look on the curve and see what reducing the current to 75% does to your output.

 

[ripped tide]

Acroholic;702948 wrote: No problem at all.

Bill, thanks for the explantation. That makes sense. It will do me as well if I end up adding my 3 AIs to the tank. I may just use them for blue accent, but If I incorporate them into the regular light schedule I know what to set them all at now, since my # of units is a multiple of the scenario I gave in the first post, it would be the same ratio.

How do you have the 9 currently arranged? Would it be difficult to incorporate the other three? I was thinking about your tank the other day and wondering how you had the lights set up. What are the dimensions of that tank?

 

[ichthyoid]

MorganAtlanta;702949 wrote: Is your 75% measuring LED output or current into the LED? The output curve vs. current is non-linear, so if it is current you are measuring, you have to look on the curve and see what reducing the current to 75% does to your output.

There was an assumption on my part that the output from the LED controller would be linear.

You could also use the PAR meter method, or look up their curve (if supplied) and extrapolate.

you raised my curiosity, so I looked a little further-

Below is a plot of flux (that's light) vs. forward current. It looks pretty linear to me, albeit not perfect (the red line). Reference source below.

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[grouper therapy]

output of the 3 fixtures / by output of the 4 fixtures = % of par from each fixture
or total number of original fixtures/ total number of future fixtures = % of par from each.

 

[ichthyoid]

Ripped Tide;702945 wrote: My head is hurting too! Its all coming to me but hard to put into words what i want to say. I'm trying to follow, and correct me if I am wrong.

A photon is a high energy electron created by radiation. In most cases, electricity is the source of energy to produce photons. As the electrical current passes through the medium used, the particles begin to rapidly speed up and begin to radiate and exchange electrons. At what point do they convert to photons and begin to emit light?

A quantum meter converts the photon into electricity. Is this similar to how solar energy is produced?

During a normal electrical current, is there still significant electron exchange? Wouldn't this cause the particles to decay over time? How could the rate of decay be determined? And if there is no decay, there has to be some molecular change, right?

And if there is significant decay, would the cheap hardware used to make LEDs wear out before the diode itself?

Dave, I don't mean to jack your thread.

Photons, to me, bridge a gap between classical physics and quantum mechanics. We can measure them, but they obey the laws of quantum mechanics. I would suggest this for some interesting reading-

http://en.wikipedia.org/wiki/Photon">http://en.wikipedia.org/wiki/Photon</a>

We can talk more tomorrow.