What’s going on everyone? As you can see, there’re lots of LED grow lights on the market today. While what to look for when buying led grow lights? Today we are here talking about serval terminologies you must know before buying led grow lights: PAR, PPF, PPFD, and photon efficacy.
So let’s put our nerd hats on, go into the classroom and talk about a couple of different acronyms that you must know.
1ST terminology, PAR or photosynthetically active radiation
From the picture below, you can see the PAR electromagnetic spectrum.
400 to 700 nanometers – that is the wavelength range of light that plants tend to use the most of. You can see, here’s the chart of photosynthetically active radiation. It is actually untrue that the green spectrum is unusable by plants. So this is, the question marks there should be resolved. Plants do use light in the green spectrum. But basically, what PAR means, it is not a measurement of the amount of light. Rather it is a measurement or a determination on the quality of that light. Is it within the photosynthetically active range or not, right?
So we can see, photosynthetically active radiation refers to the range of light that plants are using for photosynthesis.
2ND terminology, PPF or photosynthetic photon flux
Our second piece of terminology is PPF or photosynthetic photon flux. So what is PPF? It’s the measurement of the total amount of PAR or photosynthetically active radiation that’s being produced by a lighting system every single second. We can see the measurements right here are micromoles per second or μmol/s.
And what’s interesting about PPF is that it’s not telling you how much of that light is actually landing upon the plant canopy, so you can make some sort of judgment on how effective it is to grow a plant. Rather, what it’s telling you is how much is produced by the lighting system itself. The photons are coming out of the light and the PPF in micromoles per second is the reading of what’s being emitted, not what’s being received down here.
3RD terminology, PPFD or photosynthetic photon flux density
Our third acronym to know is photosynthetic photon flux density. So basically we’re just adding
the density dimension to PPF. It’s the amount of photosynthetically active photons that actually fall on a given surface per second. Think of it as raindrops. How many are hitting a given area?
So what this is? It’s a spot measurement of a specific location on a plant canopy. It’s measured in micromoles per square meter per second cause you need that area dimension to the measurement. That’s what gives you our density.
Now here’s the tricky part about this and we’re going to look at a chart in just a second, but you should take average levels here because again, it’s a spot treatment or a spot measurement. So that would be the same as if I went out into my garden and I took a soil sample of one area and found that it was deficient in nitrogen. And then I said my whole garden is deficient in nitrogen. It makes no sense to measure that way. So you have to take a spot measurement around the footprint of the light.
And so what we’re looking at above is the footprint map for the GTPanel-450 Full Spectrum LED Grow Lights. And so what you can see, this is a 5 x 5 total area, numbers all you can see was a PPFD measurement taken 6 inches away, 12 inches away, 18 inches away and 24 inches away.
With these charts, you can see how the numbers change. Let’s take a look into details together: at 6 inches away the PPFD reading is 3793, 12 inches away the PPFD reading is 2185, 18 inches 1267, and 24 inches 791. And so the light is hanging right in the middle above, which is why the PPFD readings are the densest in that area. As you move out, even at 12 inches away on these edges here, you have a 31 versus 2185. So you can see the falloff is significant and this is classic of any light.
And this is why it’s misleading to take a manufacturer’s PPFD reading that’s, that’s only probably referencing something in the middle here and saying, oh, it’s so powerful, it’s so strong. They have to provide a chart like this or else honestly you probably really shouldn’t trust them.
4TH Photon Efficacy
Our final piece, which is basically a summation of everything we just learned is photon efficacy. And the question then becomes, after we know about photosynthetically active radiation, our PPF and our PPFD, we then have to ask the question, okay, how efficient is a given lighting system, LED or otherwise, at taking electricity it’s pulling out of your outlet and converting it into photons of PAR, photosynthetically active radiation.
So what you can do is you can take PPF, which is calculated in micromoles per second like we remember, and compare it with the watt measurement of joules per second. And that will give you micromoles per joule, which is a measurement of photon efficacy. Basically what we’re saying is the higher that number, the better that your lighting system is at taking electrical energy and converting it into photons of PAR.
Conclusion: What to look for when buying led grow lights?
So after reading all above, are you clear with what to look for when buying led grow lights? To sum it up: totally 4 things you need to know, there are PAR, PPF, PPFD and photon efficacy. Hope your gardening’s going well with LED grow lights, any ideas welcome to leave a comment below or contact with us directly.
Good luck in purchasing your ideal lights and keep on growing!