What do you consider to be the highlights or key points of the research you have developed as an expert in cannabis and technical horticulture?

The role of LED light intensity and spectra in each of the various growth phases of Cannabis.

I began my research on horticulture crops in 2009. At that time, LED technology was just starting to be used for supplementing light in horticulture. I had the privilege of working in a research department where we could use LED prototypes capable of tuning both the intensity and spectra across a very wide range including UV.

One of the first lessons I learned from experiments on several different crops was that the intensity of light has a greater impact on growth outcomes than the spectra of the light. The second general finding was that higher light intensity leads to greater biomass production, but it also increases the need for other parameters, such as climate control and irrigation, to be finely tuned to fully realize the plant’s growth potential.

In the context of medicinal cannabis cultivation, four distinct growth phases and lighting conditions must be considered: mother plants, cuttings or germination, vegetative growth, and flowering. Each phase requires a different environmental setup, particularly in terms of light intensity and quality. In my research, optimization always prioritized the health of the plant first, followed by operational and investment cost considerations. 

Mother and cuttings

In commercial cannabis cultivation, young plants are often vegetatively propagated from stem cuttings to produce large numbers of uniform, genetically identical plants at a relatively low cost. The rooting of stem cuttings is a critical process, and the vigor of the mother plant providing these cuttings is equally important.

Assuming all other parameters (climate and irrigation) are properly tuned, light intensity and quality significantly affect the vigor of a mother plant. To avoid exhausting the mother plant—which is typically used to provide cuttings for multiple grow cycles—it is essential to modulate environmental parameters according to the production cycle.

In practice, mother plants are often underlit or exposed to non-uniform light. However, when growers switch to LED lighting, they often apply too much intensity and suboptimal spectra, likely due to a lack of knowledge and suppliers promoting the idea that “more is better”. While cannabis plants can tolerate high light levels, this is not necessarily desirable for mother plants.

Mother plants are the easiest to optimize, preferably with an intensity-controlled installation and a high-efficiency spectrum. The propagation phase stands to benefit the most from LED technology. Years of research on cannabis and other crops have shown that optimizing the propagation process can lead to higher annual yields (by shortening the propagation duration or creating a more vigorous start to the vegetative phase), greater crop uniformity, and improved plant quality.

Light spectra can influence the timing of rooting initiation, helping cuttings synchronize their rooting process, which results in a more uniform canopy later on. Light also affects root volume and shoot length during rooting, which in turn impacts the subsequent vegetative and flowering phases. For rooting, light intensity should be low the first few days, and if the installation allows, a dynamic light recipe with changes in the red/far-red and red/blue ratios should be applied. It’s important to note that plant responses may interact with the application of artificial auxin, and different cultivars may respond differently to light stimuli.

Vegetative phase

Light also influences the vegetative growth phase. In some cases, the vegetative phase is entirely skipped. If cuttings are well-rooted and vigorous, transitioning directly to flowering after transplanting can still allow most cultivars to develop sufficiently during the flowering phase. This approach can significantly reduce cycle time, enabling more cycles per year and higher yields per square meter annually. Additionally, it can save costs by eliminating the need for a dedicated vegetative grow space. Lighting conditions during the vegetative phase are spectrally similar to those for mother plants, but intensity increases more gradually. A well-balanced climate is needed when using efficient spectra compared to broad white light. 

Flowering phase

The flowering phase requires the highest light intensity. For fully indoor growth, very high yields (in grams per square meter of dry flower) can already be achieved with intensities below 1,000 µmol/m²/s. At intensities above 1,000 µmol/m²/s, the plant may produce slightly more weight, but only if climate settings and irrigation strategies are perfectly adjusted to the plant’s needs. However, this additional weight comes at the cost of higher electricity consumption. When growing at lower intensities, the plant’s photosynthesis is not saturated,allowing for the use of a more efficient spectrum without the risk of creating white tips.

This approach can save at least 20% on electrical consumption for lighting and likely more for climate control, while also improving flower quality (firmness and terpenes concentration). Operating close to 1,000 µmol/m²/s requires a dynamic switch between a broad white spectrum and an efficient white spectrum. Spectral tunability can save about 10% in energy while enhancing terpene expression in the flower and improving its visual appeal. A carefully designed dynamic lighting scheme can be adapted to different cultivars while steering the right climate parameters during the flowering phase.

Conclusion

When optimizing an indoor cannabis cultivation facility, it is crucial to define your goals clearly. What is the minimum yield (in grams per square meter per year) required to meet your business plan? Is a greenhouse a more advantageous option for your location? If so, ensure you understand how to supplement light properly in a greenhouse setting and have your lighting plans reviewed by an independent lighting advisor. While more light can enable higher yields, it also increases the risk of complications if something goes wrong.

Remember: more light often means more trouble when things aren’t perfectly aligned.