PAR measurement thread

[PhotonFUD]

Hey guys lots of good discussion. Hopefully all will learn lots.

You are all generally correct that both PPF and PPFD are important. PPF pertains to what the light can emit (potential) and PPFD is what the real world performance (actual) is at the point of measurement.

Which is better for horticulture? PPFD is. Why? Because as has been stated earlier PPFD takes into account the environmental factors and gives what the plant would be exposed to at that measurement point. Who knows if you are using super reflective material or have the equivalent of a black body locus affecting the light from source; only PPFD can tell you how many photons are hitting there every second on average over an area equal to 1m2.

PPF on the other hand while good for comparing the capabilities of light sources is still only one of the variables. It is the first variable to work from as it indicates the potential of the light source. Effective coverage area, reflection, light shaping, there are many other variables involved that are included in that 10-20% grow loss when using PPF to try and calculate PPFD.

The best analogy to help understand is by using the elements of rain. Light source is similar to a cloud where PPF would be the amount of water in the cloud. Photons are rain drops and PPFD is the amount of water on the ground at a specific point. Just like lights, clouds can rain down over small areas or large ones; the larger the area the less concentrated the amount of water at any point will be. Even height of clouds has an impact - the higher up the cloud is, the more evaporation of the rain drops.

At the end of the day what we want to know is how much light is at the leaf. PPFD tells us that. You can also use PPFD to compare different light sources so long as information about the environment and distance from light source is provided with the measurements.

We are used to seeing PPF/w to describe performance of leds. It is great information for building up light sources and we can then use some quick math to determine approximate performance based on some assumptions. Having said that, something like PPFD/w at distance (eg. 12", 30cm) from light source is just as meaningful.

 

[JorgeGonzales]

Hose is better. And fuck yo PPFD/W.

 

[PhotonFUD]

My kids loved that show.

And it is PPFD/w @ <distance from light>

 

[wietefras]

But thats deceiving since a Gavita states that they put out 2000 μmol/sec PPF but only get around 620 PPFD.

When you use a grow room or tent with property reflective walls, you get 700 to 800umol/s/m2 from the same light.

When doing dark room measurements, You get only 400umol/s/m2 over a 4x4' area at 36".

So which is it?

They put the fixture on or in an Ulbricht sphere and found the fixture emits around 1700 to 1800umol/s. Which is after reflector losses which will be the same for everyone.

I would rather work with a number like that and compare that to the combined PPF of the COBs.

In fact, which cares. Just pick the PPFD you want and design your COB fixture based on that

 

[PhotonFUD]

When you use a grow room or tent with property reflective walls, you get 700 to 800umol/s/m2 from the same light.

When doing dark room measurements, You get only 400umol/s/m2 over a 4x4' area at 36".

So which is it?

They put the fixture on or in an Ulbricht sphere and found the fixture emits around 1700 to 1800umol/s. Which is after reflector losses which will be the same for everyone.

I would rather work with a number like that and compare that to the combined PPF of the COBs.

In fact, which cares. Just pick the PPFD you want and design your COB fixture based on that

Welcome to the dark side, err light side!

This is why you disagree with my ~400 umoles position and exactly why I agree with you disagreeing with my position as well. I want that ~400 umoles hitting my plant leaves, not emitted from the lamp.

The problem is both numbers are used interchangeably. This is due to the "/m2/s" which both are generally 1 and are effectively cancelled out. Although both represent PAR the two will only be interchangeable, eg. 100 PPF equals 100 PPFD when 100 umoles of photons from a light source hits a 1m2 area every second.

For everything else outside those parameters you have to do some math to estimate PPFD from PPF. Much easier to get a meter.

 

[MeGaKiLlErMaN]

When you use a grow room or tent with property reflective walls, you get 700 to 800umol/s/m2 from the same light.

When doing dark room measurements, You get only 400umol/s/m2 over a 4x4' area at 36".

So which is it?

They put the fixture on or in an Ulbricht sphere and found the fixture emits around 1700 to 1800umol/s. Which is after reflector losses which will be the same for everyone.

I would rather work with a number like that and compare that to the combined PPF of the COBs.

In fact, which cares. Just pick the PPFD you want and design your COB fixture based on that

My point is that if you use real word data, you get more accuracy.. I don't care what a PPF of a light is if most of it hits a single point in the middle. When there is the rest of a 4x4 that still needs light. That's why you take the average... It's really a simple concept to get. To compair you take it from the same height and recomended height to gauge it

I've said different numbers for brevitys sake that's all, estimations. But they both show that it is PPFD that is more important.

 

[PhotonFUD]

My point is that if you use real word data, you get more accuracy.. I don't care what a PPF of a light is if most of it hits a single point in the middle. When there is the rest of a 4x4 that still needs light. That's why you take the average... It's really a simple concept to get. To compair you take it from the same height and recomended height to gauge it

I've said different numbers for brevitys sake that's all, estimations. But they both show that it is PPFD that is more important.

Well to be fair, PPF is more important to a vendor

 

[wietefras]

This is why you disagree with my ~400 umoles position and exactly why I agree with you disagreeing with my position as well. I want that ~400 umoles hitting my plant leaves, not emitted from the lamp.

No. That is something completely different.

There is no optimal value like you claim. Cannabis plants can deal with much higher PPFD than your random school textbook chart shows. This is studied and documented.

I'm saying that if you throw away two thirds of the HPS light by not having (reflective walls) you end up with a much lower PPFD. In fact so much so that the measured PPFD is completely useless in comparisons to other lights

 

[MeGaKiLlErMaN]

Well to be fair, PPF is more important to a vendor

Yeah but who cares about them? Lol I know I know it works for a single point light.. Just not multiple.. Since most commercial LED lights are like a panel

 

[MeGaKiLlErMaN]

No. That is something completely different.

There is no optimal valuebluke you claim. Cannabis plants can deal with much higher PPFD than your random school textbook chart shows. This is studied and documented.

I'm saying that if you throw away two thirds of the HPS light by not having (reflective walls) you end up with a much lower PPFD. In fact so much so that the measured PPFD is completely useless in comparisons to other lights

Look at my measurement at 3 foot for HPS... There really isn't anything to reflect after a certain distance... I consider everything under 200ppf to be meaningless IMO. Reflective wall or not it still way too low PPF/PPFD

 

[PhotonFUD]

Look at my measurement at 3 foot for HPS... There really isn't anything to reflect after a certain distance... I consider everything under 200ppf to be meaningless IMO. Reflective wall or not it still way too low PPF/PPFD

It's ok. At some point he might come around.

It is good that plants are able to handle excess light so there is lots of buffer. Only harm is maybe to the electric bill.

What's wrong with 200ppf? Assuming you could focus all the light into a 0.5m2 circle (~40cm radius), that would be 400 PPFD on average. 0.25m2 (~28cm radius) gives you 800 PPFD. It is all about how you use it.

You can also use PPF for light sources consisting of multiple light sources, it is just more math. I still point to the meter as being the easiest option as it takes the guesswork out of that 10-20% unknown factor.

 

[wietefras]

Look at my measurement at 3 foot for HPS... There really isn't anything to reflect after a certain distance... I consider everything under 200ppf to be meaningless IMO. Reflective wall or not it still way too low PPF/PPFD

That's not how any of that works. If you reflect that 200umol back it adds up to 400.

You guys can do whatever you want of course, but I felt it prudent to warn that the outcome is completely useless for the purpose you envision.

That's all I have to say about that.

 

[MeGaKiLlErMaN]

That's not how any of that works. If you reflect that 200umol back it adds up to 400.

You guys can do whatever you want of course, but I felt it prudent to warn that the outcome is completely useless for the purpose you envision.

That's all I have to say about that.

I guess I need a more reflective wall then. I have panda film which has a mild gloss. I've never had that much reflected back.. At least in my tests. Recommendations for the most reflective material?

 

[MeGaKiLlErMaN]

It's ok. At some point he might come around.

It is good that plants are able to handle excess light so there is lots of buffer. Only harm is maybe to the electric bill.

What's wrong with 200ppf? Assuming you could focus all the light into a 0.5m2 circle (~40cm radius), that would be 400 PPFD on average. 0.25m2 (~28cm radius) gives you 800 PPFD. It is all about how you use it.

You can also use PPF for light sources consisting of multiple light sources, it is just more math. I still point to the meter as being the easiest option as it takes the guesswork out of that 10-20% unknown factor.

Nothing wrong with it just wouldn't consider it useful... I'm happy with the measurements I'm getting and I will be lowering my lights eventually... Currently my lights have pushed my plants to get too big too fast... Like I'm waiting on clones but I have to cut the other plants in half to keep it manageable lol. Good stuff 1200ppfd. Eventually I'll push 1500-1800ppfd for my area... But that's after my results.

 

[Greengenes707]

I look forward to SEEING anything

 

[MeGaKiLlErMaN]

I look forward to SEEING anything

I can only see in the par range... It's a curse

 

[Greengenes707]

I can only see in the par range... It's a curse

Results funny guy. What results does anyone have?
And what PPF and PPFD was that at.
How did that compare to lower and higher ranges.

And PS...you can see outside of 400-700. And so can plants.

 

[Yodaweed]

I came to read about PAR measurements and all I read was bickering

 

[MeGaKiLlErMaN]

Results funny guy. What results does anyone have?
And what PPF and PPFD was that at.
How did that compare to lower and higher ranges.

And PS...you can see outside of 400-700. And so can plants.

Twas the joke. I'll demonstrate just give me some time

 

[PhotonFUD]

I look forward to SEEING anything

First post shows a pretty chart. At least I think it is pretty.

The title is 'PAR Measurement Thread' and I agree we should be seeing more people posting measurements. PPF, PPFD, doesn't matter as collectively we understand what they mean and can help work through the numbers.

Being a hobby, you can pick and choose what you want to believe in and do. Share knowledge, share experience, it is all good for everyone!