Using PAR instead of lumens

[NebulaHaze]

Yes, but lumens is a unit of measurement. I can say something is giving off 1000 lumens. But you can't say 1000 PARs because PAR is not a unit of measurement. Aren't you curious what your instrument is actually measuring? I think it's measuring in μmol·m⁻²·s⁻¹ which is basically the amount of photons per square meter per second, but there are other ways to measure light like W/m².

It seems like if you want to compare to journals or other growers you would want to know what you're comparing, right? Otherwise you're comparing apples to oranges.

It's like if I said the size of a ruler is 10. Do I mean 10 inches, 10 cm or 10 feet? It's unclear what is even being measured without the unit of measurement. Do you see what I'm saying?

[9fingerleafs]

I think I know how to put this in simple words. "Visible light" is a term we use to refer to the range of electromagnetic radiation that we perceive. Now "PAR" is the plant "visible light" referring to a different range of the spectrum. Many light that we see and some we don't. So just as some light bulbs are made to produce the light we see. There are light bulbs that produce light in the PAR range. Regardless of the intensity. Which nebula is asking about. And its measured in diferent units

[Vapo69]

It's measuring in µmol.m-².s-¹ if you zoom in on Amazon pic, you can just see it in the btm right I think, is that what you mean

[NebulaHaze]

Yes, thank you! I thought so and I tried looking but couldn't see it

[Vapo69]

I thought that was what you were asking lol glad I could help

[bobsakamoto]

NebulaHaze , have you found out any more about inexpensive or DIY PAR meters, or sometimes, if the interwebs is right, called quantum meters (?).

i am interested in making one and did some deep digging on it. i used to have a small saltwater aquarium about 20 yrs ago and i pretty much DIYed everything i could, bc everything about that hobby is $$$ unless you DIY. anyway, the most active stuff i found about DIYing a "ppfd measurement device" (wanna label it a PMD? ; ) ) was on aquarium forums.

i think if i could figure out what the right sensor is i could do the rest of it fairly cheaply. that's the biggest problem i've run into. i did find a lot of helpful scholarly articles on the importance of measuring PAR and some perhaps very applicable ones that were done on tomatoes....

[bobsakamoto]

i forgot something important....everything i read seems to indicate that PMDs of any type have trouble measuring LEDs properly. is that the case in your opinion? that is, what i read indicated that even the expensive PAR meters have about a 7-10% accuracy differential, which, if i understood what i read correctly means that it could be that off *on average* meaning that its true operation could swing wildly...

anyway, just wanted to get your thoughts if you had any....

[NebulaHaze]

The reason they don't work well for LEDs is they're calibrated to test the amount of light at various spectrums, then use software inside to calculate the lumens programmatically, usually based either on fluorescent light since most of the time that's what lux meters are being used for.

The type of meters that fully measure each individual spectrum without any type of calculations costs thousands of dollars and really are only used in labs for the most part. The cheaper meters aren't quite as accurate.

So for example, say a light meter measures the amount of light at spectrum at 400, 500, 600 and 700 nm (this is just an example). The light meter then "thinks" about (calculates) how much total light energy it estimates would come through with fluorescent light based on that spectrum. So the measurements taken will be great for fluorescent lights, but imagine if all the light was coming at 450, 550, and 650 nm, like what could be possible with LEDs. The meter could measure very small amounts of total light energy because it's not measuring the amount of light for those spectrums, even though there could be tons of light energy coming through in the PAR range. But if you were using a full-spectrum LED with a light spectrum is similar to the light from a fluorescent, than the light meter would be able to measure the total amount of light in the PAR range that is being delivered pretty accurately.

So the better the meter, the more data points are taken, and the more accurate the final reading, especially with non-standard spectrum lights. Pretty much all lights meters (even the $40 ones) would great for fluorescents and similar colored lights, but the better light meters are able to do more varied types of light and still be accurate.

[bobsakamoto]

nebula, thank you so much! that was SO so helpful!!! i kind of got the impression from what i read, especially in the scholarly articles, that the lower priced "quantum meters" were really just using some sort of conversion program to change lumens to ppfd.

the aquarist that i found that has had the most success DIYing one uses different tiny, colored filters (depending on what part of the spectrum he's trying to "force" the light meter to measure) placed over the sensor. he then calibrates it against one of those crazy expensive ones (apogee or li-cor i think) and reverse engineers which filter, say, measures between 450-550, and the other which measures 650 and higher.

that's why i think i could DIY something that might work by following his method and adjusting it as need be.

so do you or anyone know what type of sensor is needed?

[NebulaHaze]

nebula, thank you so much! that was SO so helpful!!! i kind of got the impression from what i read, especially in the scholarly articles, that the lower priced "quantum meters" were really just using some sort of conversion program to change lumens to ppfd.

the aquarist that i found that has had the most success DIYing one uses different tiny, colored filters (depending on what part of the spectrum he's trying to "force" the light meter to measure) placed over the sensor. he then calibrates it against one of those crazy expensive ones (apogee or li-cor i think) and reverse engineers which filter, say, measures between 450-550, and the other which measures 650 and higher.

that's why i think i could DIY something that might work by following his method and adjusting it as need be.

so do you or anyone know what type of sensor is needed?

I don't, but if you find out I hope you come share it with us! That would be such a huge thing for the growing community if there was a tutorial on how to make a more accurate way to measure light

[Iammygod]

To you as a grower there is no accurate and unexpensive way to measure PPF or YPF. you need a team and a lab with weed plants to do some researches on how weed plants react with different level of PAR as i dont think there is no such an published info. threshold of max light, the one you are looking for, depends on CO2 level. You also need to focus on VPD, Nutrient dose, temp and other factors.

First of all we need Healthy growth. I think it can be done this way:

Step 1: Hang your light, Measure VPD, and try stay in VPD ideal range. Now you are done with temp and RH. Then you need to find nutrient dose. Chack runoff PPM and it says how much change is neede for nutrient dose.

Step 2: Find the highest light intensity your plants can handle while they grow healthy by adjusting light distance.

Step 3. Supplement your plants with more CO2 than there is in free air. Perform step 1 and 2 once again.

Step 4: perform step 3 to find the highest threshold.

overall... light is not the only factor. Don't put all your energy on light. As long as you are a grower you have to focus on VPD, nutrients dose and plants shape not light. If you are trying to find the best lights dont pick an unaccurate PAR meter and dont waste your time and money. You can't try all lights specially LEDs with your PAR meter. Your par meter can't help you to reach better yields at all even if you have the must accurate PAR meter on the world(unless you want it to find out the distance from your canopy).

It's so complicated but we all are able to take full advantage of the light we have by setting up other factors of our garden. VPD is the must important one of those factore.

A PAR meter can be a useful device of you know the exact other factors and you want to set your light at best distance. You know them?

buy a LST meter... the accurate one and a accurate hygrometer to measure VPD. An Accurate PPM meter to find nutrient dose your plants need (runoff will tell you that you need higher or lower nutrient dose). With these devices you can find best distance from the light without needing to measure light.


Nebula is a pro grower because she know how to set light intensity, temp, RH, Nutrient dose, Ph and plant shape. Me like you, was putting all my energy on light. But gardening is not only about light. Dont try to find best light. Try to set best ENVIRONMENTAL CONDITIONS.

[bobsakamoto]

iammygod, thanks for all of that.

just to be clear, i am not the original poster.

i am just someone who wants to make a PAR meter if i can. and i am aware of the difficulty PAR meters have with measuring LEDs (see my original question to Nebula.)

thanks for your input!