Though your calculation of energy is completely correct, I must (again) stress the fact that photosynthesis is not influenced by the energy of the photon but by the number of photons.
When doing side by side comparisons on a limited surface you will never get a good comparison, as seldom fixtures are used as single fixtures.
There are a few things you need to take into consideration:
A wider reflector/ LED fixture has a much larger throw at a different beam angle. Even light outside the beam angle though is not wasted, but used for overlap and horizontal penetration of the crop (as long as the light goes downward)
The only light losses you have are from the wall reflection losses. All other light will reach the plants. The light losses are therefore depending on the reflectiveness of your walls, the type of reflective material and the relative amount of light that hits it.
A deep reflector or LED fixture will have less wall losses. Specifically in a single fixture application you will see that effect. However, you need to also take the fixture design into account:
A large fixture with spread LEDs will enable you to come close to the crop and deliver uniform lighting
A compact fixture or a fixture with high power COBs or high intensity individual diodes will require you to take much more distance to the crop. High output diodes are not always the right solution because of the directional output.
I know these side by sides on a limited surface are popular but they are not telling you the complete or correct story. Take our fixture for example. Most of the light it outputs at about 45 degrees to both sides, almost twice as much as straight under the reflector. Compare that with air cooled fixtures or LED fixtures without special optics or angles. The latter have more of a lambertian throw.
To illustrate the difference in reflector throws here are a few, first the HR96, then the AC/DE and then the OG8. Guess which reflectors will give you the best irradiation straight under the reflectorâŚ
So no. It will not give you any information about the PPFD you are going to get, even not in a single installation.
Let me show you a 1000W DE in a G1 and G2 tent. There are actual measurements. You can clearly see the wall influences there as well: A G1 has much more wall per surface lit, hence larger losses. The G2 is exactly twice as big as the G1. Compare these real-life application results with the grid results. G-tents comparison.pdf (2.7 MB)
And here we are not even talking about overlap, but a single application with a reflector optimized for a single lamp, which will give you even more output to the outer perimeters (the M110 SR reflector).
I am sure you are familiar with Lambertâs Cosine Law, which explains why you need a reflector with this polar diagram to get uniformity of light on the surface.
Hey Theo, thanks for the response. Maybe you can explain more what you mean when you say
photosynthesis is not influenced by the energy of the photon but by the number of photons."
Again, photons are energy. When you say something cares about the number of photons then it by definition cares about energy of that photon. I think what you might mean is that the amount of photosynthesis that occurs depends on photon count. However, that photosynthetic process would not and can not begin unless the inbound light is near resonance, i.e. has an appropriate energy(wavelength).
Also, I would be careful when stating
The only light losses you have are from the wall reflection losses. All other light will reach the plants. The light losses are therefore depending on the reflectiveness of your walls.
Every single surface in the tent is a source of loss. The walls, the tables/buckets, the soil, power chords, fans, the light fixture. If you follow the rays leaving the grow light and trace their path what you will find is that many of the rays hit many different surfaces before making it back to the plant. Also, keep in mind that these surfaces are not perfectly specular.
With ânot influenced by the energy of the photonâ I mean the following:
I am not talking about the total energy of the photons hitting the crop, but the energy per photon. Given the wavelength variable in the formula to calculate the energy one photon has, you will see that blue photons have a much higher energy than red photons, about 1.6 times as much. It also takes 1.6 times as much energy to make that photon. However, for photosynthesis that energy doesnât make any difference as it is about the number of photons hitting the plant. You need 10-12 photons (whether they are red or blue or any other color) to bind one CO2 molecule.
So were are not talking PPFD or DLI here, but just photon energy. The shorter the wavelength, the higher the energy. The higher the energy, the more dangerous the photon (Infra-red - visible - UVA - UVB - UVC - X-ray - GammaâŚ).
Iâm not a plant scientist so maybe if there is one on the forum they can correct me if I am wrong.
There are two main reasons why photosynthesis is a wavelength specific process. First and foremost, the process of CO2 bonding occurs in chlorophyll. Chlorophyll is a pigment with a well documented absorptions spectra. This alone tells us that wavelength matters.
Secondly, CO2 bonding to hydrogen happens in a two step process. Light is absorbed by chlorophyll where it frees electrons from electron donors, water in this case. Those electrons are then used in the binding process of CO2 to H2 in order to make carbohydrates. (see chemical equation below)
In order for this process to occur there needs to be enough energy present to separate the hydrogen from the oxygen and free 4 electrons. A photons energy is determined by its wavelength. Light at 400nm has single photon energy of 3.099eV while light at 700nm has single photon energy of 1.7712eV. If a process, that is only dependent on total input energy, requires, for example, an energy of 18eV to occur then we only need 6 photons of 400nm vs needing 11 photons at 700nm.
This added to the wavelength dependent absorption efficiency of chlorophyll shows why saying things like
However, for photosynthesis that energy doesnât make any difference as it is about the number of photons hitting the plant. You need 10-12 photons (whether they are red or blue or any other color) to bind one CO2 molecule.
Is patently false and can be extremely misleading to people trying to learn more about the importance of light quality in relation to their crop.
It is understandable that you get that wrong. There are much more photoreceptors in plants than just chlorophyll. Green light in high intensity white light is actually believed to be more efficient than red or blue light for example. A photon needs to have enough energy beyond the excitation level of the pigment to release an electron from the excited molecule. All other energy is dissipated.
Chlorophyll a also absorbs light at discrete wavelengths shorter than 680 nm (see Figure 16-37b). Such absorption raises the molecule into one of several higher excited states, which decay within 10â12 seconds (1 picosecond, ps) to the first excited state P*, with loss of the extra energy as heat. Photochemical charge separation occurs only from the first excited state of the reaction-center chlorophyll a, P*. This means that the quantum yield â the amount of photosynthesis per absorbed photon â is the same for all wavelengths of visible light shorter than 680 nm.
Extra energy of a shorter wavelength photon is dissipated as heat.
Now I am not saying that spectrum does not count, on contrary. But is has no effect for the photosynthetic process as such.
@Theo Thanks for the responses on both the irradiance/PPFD discussion and the photosynthesis discussion. Iâd like to work through both and continue the conversation when some time frees up. I looked over the grow light comparison with the tents that you posted. Could you tell me if each square in the representative grid corresponds to 1 measurement with the Li-Cor Par Meter?
You mean in the G1/G2 tent measurement? Yes, each number is one measurement. Moreover, they were done on a green precision grid. We used a specific color green, because if you have a white or shiny floor that greatly influences your measurement of light on a surface in a tent because of all the reflection (you get too high values). Always check if tent measurements are done with a black or green surface instead of the standard reflective material. We even went as far as doing the measurement in the tent at plant height, with the green grid at 5 ft high in the tent, diminishing the reflective surface of the tent: plants do not grow at the bottom of your room. Of course we did it with the tent closed.
Of course all measurements were done with a calibrated Li-Cor PAR meter. Thatâs the only instrument we use for field measurements. Hence the calibrated: All measurements you do must be done with a professional, calibrated meter.
Right, so what happens if I send a single photon with wavelength equal to 810nm, for example? Does photosynthesis occur? What happens if I send in light that is completely out of resonance with the absorption spectra of a plants photoreceptors?
Not much as for photosynthesis. However, it will probably warm up the plant so it has influence probably on the speed of some processes. It will not bind CO2 molecules.
I work for a lab that published a paper on plant photosynthetic health and how it relates to a wide variety of factors, PAR being one of them. We did this alongside taking lab equipment and bringing it down to fractions of the cost in handheld fashion. We combined this with a cool backend online platform for tracking variables and doing analytics to gain a really deep insight.
Some members of the lab such as myself and other people on this paper (http://rsos.royalsocietypublishing.org/content/3/10/160592) have decided to adapt this technology specifically for the cannabis space. We hope we can help this community to look at their plants, grows and managements in a more scientifically and rigorous way. This is a great use case where we could have a community project and test how these factors are effecting our grows. It really pumped me up to see this post and I implore you to read that paper and talk to me about how you would see this being used in the cannabis space.
Can we please be FAIR and add in a Plasma light? Dunno why it was not added in here⌠oh wait⌠Yes I do⌠Because it actually is better than any other light watt per watt.
Sorry but in terms of your statement that plasma is better or more efficient per watt than any other lighting technology that is not the case at all.
Take a look at the Gavita 300LEP spec and youâll see that these are meant to supplement HPS spectrums and as you can see on page 2 the PPF is listed at 300 uMole. This puts it at just 1 uMol/watt with a negligible amount of that energy in the UV regions. Check the SPD for yourself at the link below.
However if one were to desire greater amounts of UV-A/B (280-380nm) we offer a supplemental UV-Pontoon that mounts on the main light and as you can see by the specs there are greater amounts of UV-A/B than plasma produces.
Iâm not familiar with that number or company. Perhaps you have a link you could post. But plasma spectra is not going to vary much and while plasma does widen the spectrum over HPS spectra, in terms of efficiencies it comes in at a paltry 1 uMol/Joule.
there is no ânegligible amountâ of UVA and UVB in the spectrum. In fact, the ratio of UV is about the same as the sun. Do the measurements Darryl. See the results.
We never, ever say that plasma is a more efficient light source. In fact, it is about as efficient as induction lighting, which was regarded by Darryl as being more efficient than HPS, but that is a different discussion. All companies that have ever said that plasma is a more efficient light source than HPS have already gone out of business or donât sell any more. Remember IUNU?
Looking for lighting manufacturers and growers to participate in well designed study.
Studying photon densities alone does tell you much. Optimizing light requires optimizing all plant input and stresses for maximum light inputs. This will also require optimizing lighting configurations, distance from canopy and modification to all the above based on plant resonses which can occur from a few secounds to over 24 hours. Photsenthic floreences, non chemical quenching, protien production due to various gene expression all make such optimization well beyond the capibilities of a mere mortal. SO we are using machine learning, genetic algorithms and other Ai to solve the question as to what is the optimal lighting for each strain. Since energy use comes into play this also requires understanding in a big data way of your HVAC requirements based on your building/greenhouse. ie. HPS heat is a benifet in cold winters and a determent in summer. Gets A bit more complex in greenhouses which also need more realtime sunlight measurements.
All this requires a super computer or better yet quantum anealing algorithms on quntum computer like DWAVE. Start running up the tab to accomplish a good solution but collectively is entirely doable. also, should consider gird connected plants approch which is now being applied to electric use of server farms and electric vehcile charging. Cannabis consumes over 1% of all electrical usage. 2% in Denver.
Theo, I like your plasma video. I do of course take exception to the comment you make that itâs impossible to design an efficient reflector for an induction lamp and then show our light. Our reflector is a much better design than the tunnel light reflector design you show in the first image. Nonetheless today Iâm happy with what weâve achieved with our Impact Series of LED Grow Lights. I put up the Veg and Flower reports on our website which when talking efficiencies, emitted spectrums, area coverage, thermal contribution and life span, when given the choice, even I would not recommend our induction grow light over our Impact grow light.
