How to measure par ?

Blue brother

Blue brother

Well-Known Member
I'm pretty sure it's a spectrometer that I need. My apologies for the thread title but it isn't relevant.

I very much doubt I cOuld make an accurate geuss as to how much of each colour I have at different points around the room. When I look at the reflector I can clearly see the White light from the my mh and the Orange light from my hps. But a different points around the room it is absolutely impossible to tell, whether this means it is perfectly blended I don't know, but I want to find out and that's why I need a spectrometer.
 
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LurchLurkin

Active Member
Light does not travel in a particle nature. Light travels in a wave nature. Imagine you're sitting on the shoreline, watching the waves roll in and out. Light is kind of like that, except it's a 3 mile high tsunami that will rock your socks and rip into every nook and cranny that you don't have completely sealed.

If you want to try a cool experiment, go get one of those little laser pointers and tape it to a table pointed at a wall about 3 feet away. Presuming your walls are white (if not place a piece of paper where the laser hits) then take a strand of hair and place it directly in front of the laser beam.

So now you will see that you have a very bright portion of light directly behind the hair on the wall. You do not see a shadow. Even more perplexing, you will see little "dashes" of missing light in a horizontal line (provided you're holding the hair vertically).

The thing is, when the light hits the hair the original wave breaks off and starts two new waves. When the new waves are out of sync by 180 degrees they will cancel each other out. This depends on distance from the hair to the wall how well you will see them.

So you see, any object may cause light to deflect and start new waves (the same happens on either side of a hole) and they will only cancel each other out when they are out of sync 180 degrees. If you move the hair forward and back you will see that the waves change their spacing.

This does depend on the wavelength of the light, but can you hold your spectrometer perfectly still and are you willing to do this over every millimeter of the room?

Yes, common sense tells us that large objects can "shadow" others from light.

So again, rent a PAR meter, it will tell you how much "light" the plants can use at any given location as a sum of (high wavelength UV - vis light - near infrared) that plants are capable of using.

Does it make different colors? Yup, some you can't see, but the plants can use all of them and even if they're less efficient in photosynthesis (green) in reality the refraction causes the utilization to be about the same as blue light. Red light is slightly more available but causes stretching.
 
_MrBelvedere_

_MrBelvedere_

Well-Known Member
LurchLurkin said:
Light does not travel in a particle nature. Light travels in a wave nature. Imagine you're sitting on the shoreline, watching the waves roll in and out. Light is kind of like that, except it's a 3 mile high tsunami that will rock your socks and rip into every nook and cranny that you don't have completely sealed.

If you want to try a cool experiment, go get one of those little laser pointers and tape it to a table pointed at a wall about 3 feet away. Presuming your walls are white (if not place a piece of paper where the laser hits) then take a strand of hair and place it directly in front of the laser beam.

So now you will see that you have a very bright portion of light directly behind the hair on the wall. You do not see a shadow. Even more perplexing, you will see little "dashes" of missing light in a horizontal line (provided you're holding the hair vertically).

The thing is, when the light hits the hair the original wave breaks off and starts two new waves. When the new waves are out of sync by 180 degrees they will cancel each other out. This depends on distance from the hair to the wall how well you will see them.

So you see, any object may cause light to deflect and start new waves (the same happens on either side of a hole) and they will only cancel each other out when they are out of sync 180 degrees. If you move the hair forward and back you will see that the waves change their spacing.

This does depend on the wavelength of the light, but can you hold your spectrometer perfectly still and are you willing to do this over every millimeter of the room?

Yes, common sense tells us that large objects can "shadow" others from light.

So again, rent a PAR meter, it will tell you how much "light" the plants can use at any given location as a sum of (high wavelength UV - vis light - near infrared) that plants are capable of using.

Does it make different colors? Yup, some you can't see, but the plants can use all of them and even if they're less efficient in photosynthesis (green) in reality the refraction causes the utilization to be about the same as blue light. Red light is slightly more available but causes stretching.
Click to expand...

+1000k rep on clearly explaining something I've constantly struggled understanding for years- definitely an aha moment Thx
 
Blue brother

Blue brother

Well-Known Member
LurchLurkin said:
Light does not travel in a particle nature. Light travels in a wave nature. Imagine you're sitting on the shoreline, watching the waves roll in and out. Light is kind of like that, except it's a 3 mile high tsunami that will rock your socks and rip into every nook and cranny that you don't have completely sealed.

If you want to try a cool experiment, go get one of those little laser pointers and tape it to a table pointed at a wall about 3 feet away. Presuming your walls are white (if not place a piece of paper where the laser hits) then take a strand of hair and place it directly in front of the laser beam.

So now you will see that you have a very bright portion of light directly behind the hair on the wall. You do not see a shadow. Even more perplexing, you will see little "dashes" of missing light in a horizontal line (provided you're holding the hair vertically).

The thing is, when the light hits the hair the original wave breaks off and starts two new waves. When the new waves are out of sync by 180 degrees they will cancel each other out. This depends on distance from the hair to the wall how well you will see them.

So you see, any object may cause light to deflect and start new waves (the same happens on either side of a hole) and they will only cancel each other out when they are out of sync 180 degrees. If you move the hair forward and back you will see that the waves change their spacing.

This does depend on the wavelength of the light, but can you hold your spectrometer perfectly still and are you willing to do this over every millimeter of the room?

Yes, common sense tells us that large objects can "shadow" others from light.

So again, rent a PAR meter, it will tell you how much "light" the plants can use at any given location as a sum of (high wavelength UV - vis light - near infrared) that plants are capable of using.

Does it make different colors? Yup, some you can't see, but the plants can use all of them and even if they're less efficient in photosynthesis (green) in reality the refraction causes the utilization to be about the same as blue light. Red light is slightly more available but causes stretching.
Click to expand...
Thank you very very much LL what an informative post.

So by that logic my room WILL have as near perfect as I need blend of different colours.

I just didn't wAnt to find that my crop wasn't uniform from one side of the room to the other. I.e areas lacking in blue (less desirable turpene profile), and areas lacking in red/orange (less yield).

Just in case this makes a difference my room measures 3x4 ft and I have 2 600w dual arc bulbs spaced evenly. Each bulb consists of a 300w mh and 300w sodium. Working out at 50w per square foot of blue and the same for red.

Once again thank you very much for taking the time to explain that. +rep
 
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LurchLurkin

Active Member
Blue brother said:
Just in case this makes a difference my room measures 3x4 ft and I have 2 600w dual arc bulbs spaced evenly. Each bulb consists of a 300w mh and 300w sodium. Working out at 50w per square foot of blue and the same for red.
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Yes, your light will be distributed evenly enough. If you were using LED, well, that can get a bit more complicated.

The question, though, is are they getting enough light? That is subjective.

Most people claim light to be the "limiting factor" and it usually is, but I think nitrogen is also a big one. The reason I think this is because people claim to get benefits from beneficial microbes. These microbes fixate nitrogen from the air and provide it to the plant, if you were providing enough nitrogen then the beneficial microbes would form a parasitic instead of symbiotic relationship and you wouldn't notice a difference.

Furthermore, how much light your plants can utilize depends also on CO2 concentration and temperature.

" In view of these results, temperature and light optima for photosynthesis was concluded to be at 25-30 °C and ∼1500 μmol m(-2)s(-1) respectively....reflects its potential for better survival, growth and productivity in drier and CO2 rich environment."
-http://www.ncbi.nlm.nih.gov/pubmed/23572895

Albeit, they only tested up to 750ppm CO2. All of the variables are tied together and I believe there was another study along time ago that found the same temp but they used like 1200ppm CO2 and found 2000ppfd to be optimal.

So again, you need a PAR meter lol.

Also...HID is incredibly inefficient. If you really wanted to get your plants more light for their efficiency then you need to go vertical. How you do it is up to you and depends on your medium.

The reason for this is the inverse square law. Imagine your light being the source, S, in the below picture.


So the more uniform you have your plants distributed around the round bulb the more efficient your grow will be and the more light they will receive.
 
Blue brother

Blue brother

Well-Known Member
Yaaaay I was wondering how long it would be before someone mentioned old Albert. Well I'm renting a par meter next week for 3 days. I kinda wanna go buy a cmh just to ogle the numbers lol.

My experience tells me that both par and lumen count are gonna be equally important to my end product. I've seen many LEDs try and fail to produce product on par (pun intended) with mixed spectrum hid.

We could go on forever about efficiencies and inefficiencies of different lights but at the end of the day it really just boils down to what you are restricted by, price, carbon footprint, vertical space, horizontal space, temperature etc. I remember the guy in the hydro store laughing at me when I told him I ran 100w of hid per square foot, he wasn't the only one.

They don't laugh anymore.

Thanks for all the informative and insightful replies to this thread.
 
L

LurchLurkin

Active Member
Lumens don't matter brother as a measurement. They only measure visible light, plants use visible and some invisible light.


| VISIBLE LIGHT/LUMENS|
|PHOTOSYNTHETIC ACTIVE RADIATION|

So I hope that the formatting comes out right on that. Basically, measuring lumens is only some of the light that the plant can use. Par measures all the light they can use, including stuff you can't even see. Lumens only encompass visible light, and plants can use more than what's visible.
 
Blue brother

Blue brother

Well-Known Member
Lurch this is where this has me beat, hopefully you can put me right.

If a par measurement refers to the number of photons per second (within the photosynthetic spectrum)that hits a given surface, but gives no indication as to which part of the PS they come from. Then how are we to know what light the plant is receiving.

Here's an example I thought of.
In identical conditions an hps and mh could give the same par reading. But we all know that although they both have identical par readings that par will differ greatly between the 2 bulbs. 1 being mainly red and the other mainly blue. Plants grown under 1 bulb would exhibit totally different characteristics compared with identical plants grown under the other bulb. Same plant, same par reading but different characteristics and certainly a different spectral reading.

Thanks for taking time out of your dAy to school me I really appreciate it.

LurchLurkin said:
Lumens don't matter brother as a measurement. They only measure visible light, plants use visible and some invisible light.


| VISIBLE LIGHT/LUMENS|
|PHOTOSYNTHETIC ACTIVE RADIATION|

So I hope that the formatting comes out right on that. Basically, measuring lumens is only some of the light that the plant can use. Par measures all the light they can use, including stuff you can't even see. Lumens only encompass visible light, and plants can use more than what's visible.
Click to expand...
When I buy a bulb and I see that it puts out 96,000 lumens at its source I can use the inverse square law to calculate the total ammount of lumens at canopy height, below canopy is another story as foliAr penetration probably greatly reduces the intensity.
Now when I look at the bulbs spectral reading I see the majority if not all of the light comes from the 580-650 nm range. I then have enough information to make an educated guess that most if not all of those 96,000 lumens coming from that bulb will be in that range. Which is part of the PS.

I know that plants use light that is invisible. I have even capitalised upon this by using infra red for the first 20 mins of dark cycl and uv-b throughout flowering. No doubt there are many other ways that plants and growers alike use different types of light.

While I do believe that if a bulb does not put out any par then the lumen rating is useless (to us), that is not to say that a bulb that clearly does put out par should come without a lumen rating. I see the par vs lumen argument all the time, but it don't have to be an argument unless ur trying to sell bulbs. With a little research I found both measurements to be of the upmost importance.
 
L

LurchLurkin

Active Member
Blue brother said:
If a par measurement refers to the number of photons per second (within the photosynthetic spectrum)that hits a given surface, but gives no indication as to which part of the PS they come from. Then how are we to know what light the plant is receiving.
Click to expand...
Easy answer for HID, look at it(common sense applies, don't blind yourself). Does the light look "warm"? Then it's predominantly red. Does it look cool? Then it's predominantly blue. Both lights will still contain some of the "other" colors, just not in as great of concentration.

If it's LED then just look at the specs.

If you're REALLY curious here and have money/time to blow you could view the bulb through a spectrometer and diffraction grating then compare the angle between minimas to determine which spectra are present (although not their intensities).

Lumens are a measure of light intensity calibrated for the green spectrum. If you look at a photosynthesis chart you'll see that green isn't really used. In practice, however, it is utilized about as efficiently as light from the blue spectrum. This is due to reflection allowing the light to "bounce around" as well as cartenoids below the leaf surface which pass their extra energy back to the plant.

So this means that your lumen rating is based upon a spectra that can't give an accurate reading in terms of what usable light the plant is getting as the sensitivity falls off the farther you move away from the green spectrum.
 
Blue brother

Blue brother

Well-Known Member
LurchLurkin said:
Easy answer for HID, look at it(common sense applies, don't blind yourself). Does the light look "warm"? Then it's predominantly red. Does it look cool? Then it's predominantly blue. Both lights will still contain some of the "other" colors, just not in as great of concentration.

If it's LED then just look at the specs.

If you're REALLY curious here and have money/time to blow you could view the bulb through a spectrometer and diffraction grating then compare the angle between minimas to determine which spectra are present (although not their intensities).

Lumens are a measure of light intensity calibrated for the green spectrum. If you look at a photosynthesis chart you'll see that green isn't really used. In practice, however, it is utilized about as efficiently as light from the blue spectrum. This is due to reflection allowing the light to "bounce around" as well as cartenoids below the leaf surface which pass their extra energy back to the plant.

So this means that your lumen rating is based upon a spectra that can't give an accurate reading in terms of what usable light the plant is getting as the sensitivity falls off the farther you move away from the green spectrum.
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Thanks lurch uve took the time to school me on this and I really appreciate it, I'm gonna give you some rep as soon as I figure out how to do it.
 
O

oc spork

New Member
Blue brother said:
got some dual arcs coming in the next couple days and I want to know if there is any way of reading the spectrum of light at various points around the room, I hope someone understands what I mean lol. I'd like to be able to know if there were any spots where inconsistencies in the spectrum would occur due to the light from each arc not being mixed up properly.

Thanks in advance for ur replys dudes
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