LED lighting is nowadays the preferred option for the vast majority of industrial cannabis crops, mainly due to its high photosynthetic efficiency or PPE (Photosynthetic Photon Efficacy) compared to other technologies. This variable relates the electrical power (W) consumed to the amount of light emitted by the LED equipment per unit of time (umol/s). As the power per unit of time is measured in joules (J), the units of the PPE are umol/J.

On the other hand, another of the most decisive factors for the choice of this technology is the lower price of LED equipment designed for technical horticulture compared to its price a few years ago. Finally, the price of this equipment allows the cannabis industry to make significant investments in LED technology that will allow a much faster ROI (Return of Investment) than using other technologies, all other things being equal.

One of the most important details to optimize the crop is to try to ensure that the plants receive the most suitable recipe (or type and amount of light) depending on the stage of development they are at. The most suitable light recipe to encourage rooting during the first few days, which will allow optimal development, depends very much on the ratio of red light to far-red light, as well as the supply of blue light.

According to Philips PhD Céline C.S. Nicole-de Groot, whom we had the opportunity to meet on a visit to Light 4 Food during Greentech 2022, it is interesting to test “dynamic recipes” of light. A “dynamic recipe” involves changing the type of light the plants receive depending on the stage of development and it can mean an improvement of 5-7 days per crop cycle. Also, she states that “young shoots root best when you use the right combination of red/far-red lighting. A standard light recipe does not contain far-red. That means that you have to add some far-red during the propagation phase to achieve synchronized rooting”.

This practices will promote uniform root growth in length and volume, improving clone length, variables necessary for uniform growth in the vegetative and flowering phase. According to Signify, root development must be stimulated by a specific light recipe (spectrum and intensity) during the first week of propagation, which is then adjusted to stimulate the development of the clones.

Additionally, other authors, such as Marco Pepe and his colleagues at the University of Guelph, have studied in depth and compared the optimisation of light for micropropagation using machine learning algorithms. They obtained interesting information on the importance or sensitivity of different variables with respect to different treatments. In this study, red and far-red light were the most important variables for favoring root length, excluding sucrose. Sucrose was the most important variable during this experiment, used in different concentrations in the culture medium for in vitro propagation (see References to further analyze the aforementioned study):

The uniformity of the canopy of the plants is also very important when managing a crop. It is necessary to ensure that the placement of the luminaires will allow as much uniformity (or homogeneity) of light as possible. The more distance between the light source and the canopy of the plants, the more homogeneity but less intensity.

Considering the amount of investment required for LED technology, it is a priority to find the balance point in the trade-off between intensity and homogeneity. In this way, we minimize the possibility of different growth rates between plants in the same batch during the vegetative and flowering phase. Consequently, the possible inconveniences and the effort required for crop management are reduced.

References:

• Philips. Dynamic light recipe provides optimal and uniform propagation of cannabis plants under Philips LED lights. URL: https://www.lighting.philips.ca/products/horticulture/medicinal-cannabis/philips-led-recipe-provides-optimal-propagation-of-cannabis-plants.

• Pepe M, Hesami M, Small F and Jones AMP (2021). Comparative Analysis of Machine Learning and Evolutionary Optimization Algorithms for Precision Micropropagation of Cannabis sativa: Prediction and Validation of in vitro Shoot Growth and Development Based on the Optimization of Light and Carbohydrate Sources. Front. Plant Sci. 12:757869. DOI: https://doi.org/10.3389/fpls.2021.757869