Céline Nicole de Groot: “A lot of light is needed for cannabis to express its genetic performance and maximum yield”

With a vast knowledge of physics, chemistry, thermodynamics, plant science, light and sensor technology, Céline Nicole de Groot has dedicated the last 14 years to developing technological solutions for indoor horticulture, with a focus on greenhouse cultivation and other closed systems. Her experience in using light to improve plant quality led her to be selected for the Cannabis Research Program, starting a new chapter in her career in 2018, coordinating innovation projects and collaborations with universities.

A researcher at Philips in the Netherlands until the end of last month, Céline is now in a transition phase in her professional career, where she has long experience as a leader of research programs in indoor agriculture.

We met Céline Nicole de Groot in Bordeaux, on the occasion of the Science in the City event, where she was a speaker, and spoke with her about several topics, including the use of lighting technology to optimize cannabis cultivation, energy efficiency and the impact of light on humans, exploring how different spectrums affect behavior and health, such as sleep and concentration.

Céline, thank you very much for accepting this interview for CannaReporter. How did you get started working with cannabis? 

It’s very simple. I worked for Philips Horticulture for 15 years doing research and specialized in research into the quality of indoor vegetables and fruit for the vertical farming industry. In that work, I showed how we can use light to manipulate the quality of vegetables such as lettuce, rocket and other plants in the brassica family, and increase the vitamin C, carotenoids, flavonoids and volatile compounds in basil, etc.  So when Philips started a research program on cannabis six years ago, I was naturally chosen to participate in this research program because cannabis is produced by its compounds and I was the only researcher at the time who had knowledge of what we can define as a research topic to work on metabolites and compounds.  So that was a bit of my experience in other cultures and I naturally moved into cannabis research, which was very fascinating.

And before that, when you were a child, do you still remember what you wanted to be when you grew up?

Yes, I remember it very well. I always had a lot of questions and I would ask my parents, “Why this, why that?” I always needed to understand how things worked. And obviously I had a researcher’s mind and having been raised and educated in France, I ended up studying mathematics and physics. So I’m now a researcher in physics. I have a PhD in quantum physics and it was only because of Philips that I’ve been able to focus on other subjects. It’s always good to work for a big company because I do research on all sorts of topics and I’ve done a lot of research on different things. And at one point I needed someone to start research on plants and there were no photobiologists around and I volunteered. And the first question was, what does the LED do
to plants? 10, 15 years ago, nobody knew, because it was a novelty. Even at university, the professors had never tried LED lighting for growing tomatoes or any other plant. They had no idea what the spectrum does, what the intensity does, the photoperiod… So, everything had to be discovered.

And did you study this part in your physics course or was it later?

I am self-taught in plant physiology. So I was at Philips when I started doing research on plants. I only studied physics and mathematics at university.

And then you learned everything from scratch?

I learned from scratch. I learned from students at the best university in the world for horticulture, which is Wageningen University. We had students coming in, so I would guide them on the technical side, how I think the subjects should be researched, and they would guide me on how research in plant physiology is being done, because they have training for that. So it was a collaborative exchange with the university, and the professor at the university also helped us to advance the research. And after 15 years, I think I learned everything on my own. By doing — which is the best thing.

So you were saying that, before, people didn't know what LED could do for plants.

Exactly.

So they used another type of light?

Yes. Artificial light had been around for some years for growing and producing plants or for studying them in university laboratories. Fluorescent lamps, HPS [High Pressure Sodium] lamps for greenhouses or plasma lamps were also used, sometimes, because they imitate sunlight well; for research purposes they are very useful. Then, when LEDs also started to be used in commercial production facilities, the university naturally wanted to start doing research on them, because LEDs are quite different from hanging lamps.

What is the main difference?

There are two main differences: the biggest, in my opinion, is the thermal radiation. So, fluorescent lamps and HPS lamps have very low efficiency. The electrical energy is converted into photons, but most of the conversion is lost in heat, which is usually also radiated to the plant. So we have a different climate, which is also created by the luminaire. Light is not just made up of photons, but photons and heat, whereas LEDs have a different technology and produce the light in the right direction, but the heat goes to the back of the LED and is released and dissipated there, not going to the crop. So that's the first difference. And the second is, of course, the fact that with LEDs you can generate a discrete spectrum. So instead of having a very broad spectrum, like sunlight, we have a peak of red, a peak of blue… We have the LED which can be green, or have all the colors of the rainbow if you want, and the spectrum is totally different and in particular we can also have different shades of red, different shades of blue, but we also have the far red, which is also very interesting because it is not in a spectrum visible to the human eye, but it is apparently absorbed by a photoreceptor in the plants, which had a big effect on the plants when we used this LED.

And also because it saves more energy than other bulbs.

Exactly. The conversion of electrical energy into photons is much more efficient with LED.

Why? Because of technology?

It's just a technology. It's a semiconductor, it's a completely different way of generating photons.

And how does this apply or to what extent is this revolutionary for cannabis plants or cannabis cultivation?

Well, the cannabis plant loves light, it needs a lot of light. This means that when you use HPS, as this is an old technology, you need to have a very powerful HVAC (Heating, Ventilation, and Air Conditioning) system to remove the heat generated by the HPS lamps. So, managing the HVAC is more difficult. Normally, with LEDs, the HVAC management is completely different, so it is easier to create a good and stable environment, and that is what, anyway, the HVAC expert says, that working with LEDs makes the operation of the facilities much easier, especially when it comes to indoors.  Also, in low ceiling situations, the lamps can be closer to the plant, which was not possible before with HPS, because the heat is so strong that it would burn the top of the plant, so you can also get much closer to the plant. And the advantage is that the intensity of the photon radiation will be higher. Of course, you have to make sure that the uniformity is good as well. But with LED, you can get a higher photon flux than before and use less energy. For example, we found several growers who had very large facilities and they had a power limitation, because there were too many kilowatts coming into the facility and they didn't have that possibility. But when they switched to LED, they were able to meet all the power limitations and that was no longer a problem.

And why do some companies continue to grow cannabis with other types of lamps and not LED?

You mean with HPS? Well, first of all, if companies already have an HPS installation and everything is working well, and if the growers have finally figured out how to manage everything and there is a lot of knowledge, it is easy. Changing things is never easy because, basically, you have to relearn how to grow from scratch. You have to reconsider how you are going to manage the climate, how you are going to manage the airflow, how you are going to do the irrigation strategy, what photonic flux you are going to choose, what spectrum… Sometimes we try not to talk too much about this, because the intensity is the most important factor. And then the grower wants to have the same quality as with HPS, but with HPS you had a mix of different environmental conditions because of the heat, the radiation, the way things were. So, you can get a similar quality, but you have to look for it and we are helping you on that path.

And maybe some companies are still cultivating in HPS because the producers' experience is with HPS. It could be difficult to change all the procedures.

Yes, they have to produce, they can't stop everything and spend a year on R&D to switch to LED. They want to keep producing, producing, producing. The switch to LED is not always easy, that's why we try to help.

What are the main advantages of making this change?

The main advantage is that it is sustainable. We have to look to the future, because, for example, Philips has stopped producing HPS lamps; they will go out of business. No one will produce HPS for a while now, because it consumes too much electricity for the amount of light it produces. So very soon there will be a cannibalization of LEDs for all light sources.  And they know this; they know this and they were already panicking when they heard that Philips stopped producing and selling HPS last year. There are still some companies that are picking this up because they see that some people want to hold on to this old technology, but I don't think it will last for many more years. In the meantime, everyone is learning how to grow with LEDs and those who haven't made the switch are behind the technology. The main advantage is, of course, less electricity consumption, less energy, and the main energy consumption in a cannabis farm is light. You need a lot of light for cannabis to express its genetic performance and its maximum yield.

Let me read this interesting sentence from your LinkedIn profile: you say that you are an “expert in the interaction of light with living materials and organisms, humans, plants and algae”. I am also interested in this topic and the interaction of light with humans. And you also said that in the case of cannabis, the spectrum is not as important as the intensity of the light.

Depending on the intensity you want, the spectrum can be different. So, to rephrase, we found some spectral effect, but at the young plant stage, so when the plant is young, the spectrum can be optimized to achieve certain goals, to keep the plant from stretching too much or to keep the plant more compact, to give it more vigor, for example. This works for all crops, not just cannabis, by the way. And as cannabis flowers, we didn't see a strong spectral effect on compounds or yield, whereas with intensity, we saw a clear effect on yield. That's why when I compare spectral effect and intensity, intensity is number one.  It is this that we have to pay attention to and that we have to focus on, not the spectrum.

What about the interaction of light with humans?

We have studied this at Philips for years. At Philips, humans have been studied much more than plants. I personally haven't done a lot of research on the human eye, but I had colleagues in my group who were doing that. So, for example, one piece of work that I really like is the effect of the light spectrum on the ability to concentrate or relax, for example. We have warm white or cool white. We have developed a lamp that allows you to use the settings to have a cooler white, for example, which will help you concentrate, and another lamp that will help you express your creativity better. But the amount of blue in the light is also important, especially for people who use screens a lot. We have studied a lot the effect of melatonin on sleep, for people who have trouble falling asleep. I didn't do the research, but we did research with universities to understand how the human eye perceives light, when it has an effect, what you do to avoid not being able to fall asleep, etc., and light plays a very important role. And now that most people are spending time on screens until very late, before bed, that's actually very bad for your eyes. It's been shown by scientists, by data and experiments in hospital settings, and there is a very pronounced medical effect.

Because it interferes with the circadian rhythm, right?

Yes, we can also use it to change our circadian rhythm, for example.

If we change the spectrum.

Yes, if we want to adapt our circadian rhythm, for example, if we are sleepy but want to stay awake instead of falling asleep, then we can train ourselves to use blue light to stay awake. (laughter) That works too.

And if we want to fall asleep, maybe more yellow...

The ideal is to be in the dark, but if we remove the blue, it's already good.

One thing that has been intriguing me is that many cities around the world, and especially in Portugal, where I live, are changing their street lights from old bulbs to LED bulbs. But when they changed this street lighting, they replaced the yellow light with white light from the blue spectrum. I recently took some photos from the plane. You can see the difference between places where the lights are still yellow and soft and other areas where, honestly, for me, they are sometimes even harsh on the eyes. How do you see this change?

Well, it's not really my area of ​​expertise, but I recognize what you're saying. I've noticed the same thing because right behind my house, they built a parking lot and put some LED lights in it. And I've explained it to them several times and many people have complained about it. The intensity is too high. And why? Because cold LEDs have a lot of blue and the human eye is extremely sensitive to blue, in fact. And they didn't take that into account. They just measured the amount of lux (the intensity measurement unit of light for human application). But yeah, they didn't realize that the amount of lux doesn't necessarily represent the sensitivity in the blue area of ​​the human eye, and I think some of us are very sensitive to light. I am; when I have too much white light in the middle of the night when I go outside, it hurts my eyes a little bit, because I'm more sensitive than other people. I think they could really reduce the intensity, and they did reduce it a little bit, because people complained that it was too intense. But they could reduce it even more, in my opinion. So it's all about adjustment; people have to learn to adjust this correctly.

Not only the intensity, but also the spectrum. Will there be an option to have more yellow light instead of bright white light? Are there LEDs in the yellow spectrum?

Yes, yes, there are warmer LEDs.

So why don't they choose them?

That, I don't know. That's not my area of ​​expertise. It's very difficult for me to answer that question, why these choices are being made. At home, for the garden, you can buy warm white. I'm sure of that, because I use warm white myself, so yes, you have to look at the colour temperature. If it's 2.700 Kelvin, I think it's quite pleasant.

I do it too, because I care about lighting, but I've noticed that many people don't. They don't even notice it, or at least they're not aware of it.

Some people are more sensitive to the color of light than others, yes.   

Have you also noticed, and this is just out of curiosity, the cars that drive at night?

Yes.

Are you also having trouble driving at night now that LED headlights in cars are so white?

No. It doesn't bother me, because I know how it works, so I focus my vision. I never look directly at the lights of other cars. I change the focus point and try to look at the dark area. You can also use special glasses, I think, which can reduce the intensity and you don't lose the contrast.

Coming back to our plants, the cannabis market is growing all over the world. Many, many companies are producing for companies that are just starting out from scratch or that are just starting to build facilities. What would be your advice regarding lights?

Well, it all depends on the business model that the producers have in mind, as I said earlier during the conference this afternoon. What is the objective? What are the genetics? How much do you need to produce, at least, for the business to be successful? Because if the producer can sell his plants and all his production, and only needs to produce 500 grams per square meter, per cycle, he doesn't need an extra 2000 μmol (micromole) of lighting installation, for example. He can use a little less and then, with the right genetics, he can even produce more like that.  It all depends on the desire and investment that the person wants to make.  So we have a whole questionnaire for producers to help them in this process, because we saw in our data those who made the wrong choice and it didn't work, and those who made the right choices and it worked.  So we know the situations from our database of previous clients. We know what works and what doesn’t; that’s the main reason, really. People like to work with us because we’ve worked all over the world with high-tech facilities, but also low-tech ones, like in Colombia, with very low-tech farms.  We have been in many different situations, so we can adapt and have enough information to help with any type of request.

Therefore, they have a worldwide presence.

Yes.

And how many companies are you working with in Portugal?

My colleague Sabrina [Carvalho] might be able to answer that question better. She is Portuguese and is also responsible for that area. I don't know how to answer that.

And what are your plans for the future?

Well, I'm in France today because the first symposium on medicinal cannabis is going to be held in the country, something that has never happened before. And I think it would be great if I could be part of the birth of a bright future in developing and helping growers in France to grow not only medicinal cannabis (which is always under discussion now because it hasn't been voted on in the European Parliament yet), but also hemp. There are a lot of hemp growers and, to be honest, I found outdoor hemp to be of very low quality. There's a lot of loss and the climate is changing. They have a lot of problems. It's a lot of work to grow outdoors and when you lose half your yield, it's really depressing. So I'm looking forward to helping them grow indoors and advising them on how to do it in the most cost-effective way to improve quality and yield.

Did you know that in Portugal it is prohibited to grow hemp indoors or in greenhouses?

I didn't know, but I heard that yes, yes. Now that you mention it, yes.

And just two weeks ago, the Court of Justice of the European Union ruled in a case in Romania that Member States must, or at least in this case Romania must allow this producer to grow hemp indoors and hydroponically. So the regulations are very different across the countries in Europe. How do you deal with that?

Personally, I don't have to deal with that because I'm not a grower, but yes, we try to adapt and we know that things change every year. The cannabis and hemp domain is always changing.  We are not yet in cruise control (laughs) and it's not something static. We just have to adapt, be vigilant and do the best we can at this moment.

What would you like to see regulated in Europe? Perhaps a common regulation for all countries would make things easier.

It would also be good to give producers the possibility to live off production, because it is very dangerous to produce hemp outdoors; Botrytis cinerea [“gray mold”] is dangerous because, especially if we smoke the hemp flower that contains Botrytis, we can create a big problem in the lungs.

The same applies to cannabis, flowers, whatever type of cannabis.

And indoors, the climate is usually better controlled and it is easier to avoid Botrytis, I am sure of that. I think that for the consumer, it is crucial that there is good quality control of any product that is put on the market. But the same goes for food, for other horticultural crops. There are many other things that go wrong with other crops, with pesticides or other contaminants, heavy metals, that get into the product. Some people don't like having this increased control, but if we at least give them the means to grow correctly, it is a start. That is what I want them to have.

It's a good wish. At least it would make the products better. 

Yes, I loved my research on quality; I looked at the quality of many crops – shelf life, taste, and so on. So the plant can really go in all directions. It has a genetic potential and the environment in which the plants are grown will determine its final quality. So it is possible to do some manipulation within the genetic capacity of the plant. I know that, and that goes for all crops, not just cannabis. I am a perfectionist; that's why I became a scientist, I guess. I like to have everything at an optimal level, but also safe. Safety, I think, is a big concern with cannabis, and hemp, too.   

You mentioned seed banks, the importance of genetics and the collaborations you had, for example, with Sensi Seeds and Paradise Seeds. Would you like to talk a little about that?

Sensi Seeds and Paradise Seeds are really committed to innovation and research. We are part of the consortium for research and testing new genetics with Paradise Seeds under the MCPIR (Medical Cannabis Platform for Innovation and Research) program in the Netherlands. In fact, Sabrina is leading that project to get the data, and the collaboration is going very well. Sensi Seeds is also doing research with them, and we are transforming their facilities. They are moving from HPS to LED, and we are helping them with that, but we are also discovering new things – they are investigating new genetics, they are doing medical research, in real hospitals, and so on – and we like to follow them, to see if light can play a role in that research, and I think it does, because next to genetics, light is the most interacting environmental energy.

And genetics are also important in the end.

Yes, because the cannabinoid and terpene profiles are different, which creates a different medicine and a different application for the patient, but even for recreational purposes, genetics are important.

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Laura Ramos

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With a degree in Journalism from the University of Coimbra, Laura Ramos has a postgraduate degree in Photography and has been a Journalist since 1998. Winner of the Business of Cannabis Awards in the category "Journalist of the Year 2024", Laura was a correspondent for Jornal de Notícias in Rome, Italy, and Press Officer in the Office of the Minister of Education of the 2018st Portuguese Government. She has an international certification in Permaculture (PDC) and created the street-art photography archive “What does Lisbon say?” @saywhatlisbon. Co-founder and Editor of CannaReporter® and coordinator of PTMC - Portugal Medical Cannabis, Laura made the documentary “Pacientes” in XNUMX and was part of the steering group of the first Postgraduate Course in GxP's for Medicinal Cannabis in Portugal, in partnership with the Military Laboratory and the Faculty of Pharmacy of the University of Lisbon.

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