Is PAR Just Another Gimmick?

This is my first post in several years. Just getting back into the indoor gardening scene, and I’m already going to piss off a bunch of people on this forum. I got excited about new technologies since my last grow, but I fear it’s all just another marketing stunt. Here it is.

Can we all just agree that PAR is almost as worthless as Lumens? Someone please correct me if I’m wrong, but PAR is nothing more than a measure of lumens between 400nm and 700nm. Without knowing which specific frequencies of light have what level of intensity, what does a PAR rating really tell us?

In the PAR spectrum, plants really want frequencies of light centered around (in nanometers) 430, 445, 450, 475, 640, 660, and a few others in trace amounts. If your brand new $800 LED fixture pumps out a zillion ppfd at 550nm but almost nothing at the previously mentioned frequencies, then you would be wasting your money on a plant cooker. Yet it would still look great on paper compared to all those low-PAR models.

Feel free to hate me. Just be prepared to back up what you have to say. I would love to hear from those who have been growing since the dawn of HID, and especially those who have moved on to newer technologies.

im not sure what everyone else has been doing but i switched from hps to led and i only measure the ppfd that the flowers are getting with that nice instrument that apogee makes. when i bought a light i only really paid attention to how efficient it was. the light said 3 μmol/J. I havent heard any light companies brag about par rating since lumatek was talking about these "special hps" bulbs that have bla bla some high number par rating

You normaly have a spectrum chart wich tells you the levels of each frequency. They normaly use ppfd too like xox says. The led grow charts that be in the lights description should be like this one, with the main bulk of frequencys being in that part that the plants use mostly. Diffrent lights will have slightly diffrent wavelenghls being more or less. Having higher or less of certain frequencys can manipulate the plant in diffrent ways. So if you wanted something specific eg like mostly massive flowering, or more streatching, or more compact growth you can look for certain lights spectrum combinations that will do that. But most try to get as close to natural sunlight as they can (perhaps a little less blues and more reds for indoor plants and beter yields). Probably one of the grow light manufactures on here will be able to explain better, and help you more with your questions.

maybe im wrong af but i always assumed that a umole meter or a par meter measured the amount of photons being emitted within a certain nm range of the light spectrum
and a luxx meter is measuring the amount of visible light that the light source is emitting? like its measuring light intensity itself not photon output.
or maybe im just wrong af i Dunno hopefully someone more experienced can chime in

xox said:

im not sure what everyone else has been doing but i switched from hps to led and i only measure the ppfd that the flowers are getting with that nice instrument that apogee makes. when i bought a light i only really paid attention to how efficient it was. the light said 3 μmol/J. I havent heard any light companies brag about par rating since lumatek was talking about these "special hps" bulbs that have bla bla some high number par rating

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Please tell me more about this Apogee instrument. HPS to LED is a big jump, and I'm all ears.

I assume it's in reference to something like this:

secretmicrogrow420 said:

maybe im wrong af but i always assumed that a umole meter or a par meter measured the amount of photons being emitted within a certain nm range of the light spectrum
and a luxx meter is measuring the amount of visible light that the light source is emitting? like its measuring light intensity itself not photon output.
or maybe im just wrong af i Dunno hopefully someone more experienced can chime in

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I thought that light intensity was the same thing as photons. Am I missing something?

Fangthane said:

I assume it's in reference to something like this:

https://www.amazon.com/Apogee-Instruments-DLI-400-Integral-Photoperiod/dp/B09QXVX2BT/ref=sr_1_9?crid=3467UUEZJVRQP&keywords=apogee%2Bpar%2Bmeter&qid=1700532850&sprefix=apogee%2Bpa%2Caps%2C1393&sr=8-9&ufe=app_do%3Aamzn1.fos.17d9e15d-4e43-4581-b373-0e5c1a776d5d&th=1

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You had to send me down that rabbit hole, didn't you? If I am understanding correctly, the Apogee can produce a graph with it's measurements? This would be a game changer since my last grow.

Lux is a measure of the intensity, as perceived by the human eye..

FNG Grower said:

This is my first post in several years. Just getting back into the indoor gardening scene, and I’m already going to piss off a bunch of people on this forum. I got excited about new technologies since my last grow, but I fear it’s all just another marketing stunt. Here it is.

Can we all just agree that PAR is almost as worthless as Lumens? Someone please correct me if I’m wrong, but PAR is nothing more than a measure of lumens between 400nm and 700nm. Without knowing which specific frequencies of light have what level of intensity, what does a PAR rating really tell us?

In the PAR spectrum, plants really want frequencies of light centered around (in nanometers) 430, 445, 450, 475, 640, 660, and a few others in trace amounts. If your brand new $800 LED fixture pumps out a zillion ppfd at 550nm but almost nothing at the previously mentioned frequencies, then you would be wasting your money on a plant cooker. Yet it would still look great on paper compared to all those low-PAR models.

Feel free to hate me. Just be prepared to back up what you have to say. I would love to hear from those who have been growing since the dawn of HID, and especially those who have moved on to newer technologies.

Click to expand...

I agree with you and I've mentioned this a few times on here.

There are lots of frequencies in the PAR range that the plant doesn't use but still register and raise the PAR output reading so much ado about nothing imo. You need much better equipment than a PAR meter to know exactly how much of each wavelength is in that PAR zone and the folks that make the lights generally have that to tune their offerings.

I just use the light meter in one of those 3-in-1 plant probes to make sure the intensity of the bulb I'm using is high enough for the growth stage and adjust the height as needed. Did an experiment once with 3 different 1000W flowering bulbs to measure output at 1, 2 and 3ft distance and got quite a range. With quality bulbs like Hortilux SHPS I know the spectrum is going to grow great plants so just need to know it's not so close it'll fry them or too far away so they don't get enough. I'll put pots on boxes or move them closer so they all get the same amount of light.

Good enuf.

Fangthane said:

I assume it's in reference to something like this:

https://www.amazon.com/Apogee-Instruments-DLI-400-Integral-Photoperiod/dp/B09QXVX2BT/ref=sr_1_9?crid=3467UUEZJVRQP&keywords=apogee%2Bpar%2Bmeter&qid=1700532850&sprefix=apogee%2Bpa%2Caps%2C1393&sr=8-9&ufe=app_do%3Aamzn1.fos.17d9e15d-4e43-4581-b373-0e5c1a776d5d&th=1

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The very first paragraph has this interesting tidbit in it.

DLI-400 SUNLIGHT DLI METER: Gives research-grade measurements of PAR (PPFD), DLI and photoperiod in a low-cost model calibrated for measuring direct sunlight and some broadband grow-light sources only (MH, HPS).

Not made for LED it seems.

FNG Grower said:

Please tell me more about this Apogee instrument. HPS to LED is a big jump, and I'm all ears.

Click to expand...

not much to tell you hold it under your light near the canopy and it gives a measurement of the light intensity ive been using that to dial in the height of light so i can get maximum light at the canopy without burning the plants in a co2 enriched room. better than guessing with the back of my hand and hps light


i also got a pulse pro that measures spectrum but i cant speak for how accurate that is.

FNG Grower said:

plants really want frequencies of light centered around (in nanometers) 430, 445, 450, 475, 640, 660, and a few others in trace amounts

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That's a pretty specific claim. Do you have proof for that?

Because I know the boatload of research showing that all wavelengths contribute to photosynthesis. The McCree curve show here is the product of that research. Sure you can argue that green might be 10 % worse than red or whatever but that are details that don't matter much in practice (where you have 30 % loss on walls etc.).

FNG Grower said:

This is my first post in several years. Just getting back into the indoor gardening scene, and I’m already going to piss off a bunch of people on this forum. I got excited about new technologies since my last grow, but I fear it’s all just another marketing stunt. Here it is.

Can we all just agree that PAR is almost as worthless as Lumens? Someone please correct me if I’m wrong, but PAR is nothing more than a measure of lumens between 400nm and 700nm. Without knowing which specific frequencies of light have what level of intensity, what does a PAR rating really tell us?

Click to expand...

PAR is not a measurement. PAR is a way referring to light that falls within the 400-700nm range. A lumen is a measurement and it indicates how much light is generated by a light source.

If PAR is light that plants can use, "human visible light" would be how you would describe what lumens deal with. PAR is for plants, lumens is for humans.



The amount of human visible light is usually measured in lux. Lux tells us the amount of lumens hitting a square meter in a second. When measuring light for plants, we're interested in the amount of PAR hitting the plants. When using a PAR meter, it measures the number of photons hitting a square meter in a second which is called the photosynthetic photon flux density ("PPFD"). That value is expressed in µmol ("micromols").

You can see that the PAR spectrum covers a wider range than the human visible light spectrum. If we're using an instrument that reads the human spectrum, can it be used to figure out what that means in PPFD? For most growers, I would argue that you can get close enough.

And how do you do that?

You have to use a conversation factor. For a "standard" LED grow light, a factor of 0.015 works well enough. This concept and a conversion table are discussed in the attached PDF.

You bring up the point that a PAR meter does not tell us which frequencies/colors of light are hitting the plant. That's correct. A PAR meter does not do that. A spectrophotometer does that.

The color of light controls/influences plant shape ("morphology") and growth. Blue photons inhibit cell expansion so plants will tend to be short and compact, will have more stems and leaves, and less internodal space. Red photons encourage cell growth.

In terms of yield and crop quality (the ration of flower to plant mass), overall, yield is more influenced by the amount of light/photons.

imo if a led has only 3000k leds and a real small percentage of ir uv etc and another one has 3000k + 3500k + 6500k +ir +far red + uv the second would grow better

in the variety is the taste

lets remember that a 3000k led emmits from blue to green to red so there is no such thing as a led only emmiting 550nm it will emmit almost a full spectrum (im not talking bout ir uv and far red as those emit a single spectrum or nm)

OldMedUser said:

The very first paragraph has this interesting tidbit in it.

DLI-400 SUNLIGHT DLI METER: Gives research-grade measurements of PAR (PPFD), DLI and photoperiod in a low-cost model calibrated for measuring direct sunlight and some broadband grow-light sources only (MH, HPS).

Not made for LED it seems.

Click to expand...

There are three models for sale on that page. Per your quote, the DLI-400 is for sunlight and, MH, and HPS. The DLI-500 measures the PAR spectrum (400-700nm) and the DLI-600 measures 400-759, referred to as "ePAR". Per the tech support people at Apogee, the main cost driver is the sensor - the broader a spectrum that's sampled, the greater the cost of the sensor.

Not all sensors are created equal, unsurprisingly. The attached PDF might give some insight into what you get when you pay for, say, an Apogee vs a Hydrofarm (it would not surprise me if that the same sensor/sensor design is used in the other low priced PAR meters on Amazon but I haven't seen the results of a teardown).

Delps8 said:

There are three models for sale on that page. Per your quote, the DLI-400 is for sunlight and, MH, and HPS. The DLI-500 measures the PAR spectrum (400-700nm) and the DLI-600 measures 400-759, referred to as "ePAR". Per the tech support people at Apogee, the main cost driver is the sensor - the broader a spectrum that's sampled, the greater the cost of the sensor.

Not all sensors are created equal, unsurprisingly. The attached PDF might give some insight into what you get when you pay for, say, an Apogee vs a Hydrofarm (it would not surprise me if that the same sensor/sensor design is used in the other low priced PAR meters on Amazon but I haven't seen the results of a teardown).

Click to expand...

Still more than the average home grower needs and can cost more than a quality LED light that will grow plants just fine without testing.

I guess if someone has money to burn and likes to micro-manage their growing something like that could seem like a necessity but is way down on my list of things I need or want.

A lot of people make growing a plant a lot more complicated than it really is.

OldMedUser said:

Still more than the average home grower needs and can cost more than a quality LED light that will grow plants just fine without testing.

I guess if someone has money to burn and likes to micro-manage their growing something like that could seem like a necessity but is way down on my list of things I need or want.

A lot of people make growing a plant a lot more complicated than it really is.

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Without measuring, how do you know you're not giving the plant 'too little light?