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4.32 μmol/J?

We decided to launch the #Pozeen #CannaUniversity program. The purpose of the program is to provide educational information to the public. And we would like to start with photosynthetic photon efficacy (PPE) as our topic.

In the recent two years, thousands new grow light suppliers have flooded into the hydroponic grow industry; and everybody is trying to over-marketing the term PPE, PPF/W or μmol/J. The message they want to deliver to the growers is the higher the μmol/J, the more advanced technology their grow light is and the higher yield. I once came across an advertisement by a light manufacturer who states 4.32 μmol/J for their grow light, which astonished me. And it’s the time to unveil the truth behind.

The μmol/J comes by PPF (μmol/m2/s) divided by watt. To achieve a higher μmol/J, you need a highest possible μmol/J and lowest possible watt. To make it simple, all the following analysis is based on LED technology at finish light level.

Let’s start with watt which is easier to understand, measure and verify.

Technically, the watt is the actual power draw by the light fixture, and it comes by output current times output voltage divided by efficiency of the driver (I*V/e). Once the circuit layout is finalized, the output current and voltage are always static numbers and won’t change at all. The watt will primarily depend on the efficiency of the driver.

Although LED driver is a very complicated electronics device comprised of hundreds of components; all LED drivers are using very similar components like transformers, chips and capacitors from a few suppliers. That is why the efficiency from driver to driver of same watt has not much difference.

Typically, a 600W driver can be 95% efficiency at 240VAC, while a 100W driver will be about 89% efficiency at 240VAC. There is no way that a Mean Well driver is better performed than a Powerland driver which Fluence uses or ProPower driver that Pozeen uses. The only thing makes the driver different from each other is the reliability since there are a lot of components inside.

And the watt can be easily measured by a power meter to verify if it matches with the cut sheet of the driver.

Compared to watt, the PPF can only be measured or verified by professional instrument like photometric sphere with proper sensors built-in, which most growers have no access to. And this is the grey area that the supplier can play or manipulate in.

Technically, the PPF is the quantity of photons emitted by LED chips; the bigger the better chips you use, the more photons they generate and the higher PPF you get. Fluence does not produce LED in house, but outsources from Samsung and Osram; so do Gavita, Luxx and etc. Again, the difference between different light manufacturers is very limited if they use the same diodes.

For example, Osram GH CSSRM4.24 diodes have 5.74 μmol/s at 1.4W which equals to 4.10 μmol/J; Samsung LM301H diodes have 0.56 μmol/s at 0.2W which equals to 2.8 μmol/J. The light fixture will not be able to generate higher μmol/J than LED diodes after the heat loss by LED diodes (typical 96%) and efficiency of an LED driver (typically 94%). Since white LEDs have way lower efficiency as red LEDs, it won’t be hard to find out the highest μmol/J of a grow light is full of red LEDs. That is 4.10 μmol/J times 96% which is the heat loss by LED diodes and times 94% efficiency of LED driver which comes to approximately 3.69 μmol/J.

The sad fact is no growers can verify the actual PPF in the field because they have no testing instrument; they can only rely on the data the manufacturer states on the cut sheet or send the light fixture to third-party testing laboratory to verify. The sadder fact is most manufacturers, from tier 1 down to tier 2 and 3, are playing and exaggerating the numbers to present a μmol/J that never be delivered.

While most manufacturers are pursuing a higher μmol/J, the question to all manufacturers is: DOES THE μmol/J BENEFIT ANYTHING TO PLANTS? The answer is obvious: NOT AT ALL. The things help plants to grow and yield are PPFD and spectrum; we will discover this in future topics.

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