Cannabis lighting is a hot topic among growers because it can have a major impact on yields and quality. There are a variety of lights that are utilized to meet the plant’s needs. Cannabis is a short-day plant, so it needs twelve or less hours of light during its vegetative growth stage and more than twelve hours of light to trigger and sustain the floral growth stage. Cannabis also grows better with more blue light during vegetative growth and more red and far-red light during floral growth.

Traditionally, cannabis growers utilized metal halide (MH) lamps for the vegetative growth stage and high pressure sodium (HPS) lamps for floral growth. However, these lamps tend to run hot and use a lot of electricity. LED lamps are the more modern alternative. While early models of LED cannabis grow lights failed to deliver, newer models have had impressive results. LED arrays can be customized to target different intensities and colors (spectrums) of light, they require less electricity, and have long lifespans.

Juvenile cannabis plants, clonal cuttings, and sprouting cannabis seeds don’t really require special light. Growers will typically raise them under fluorescent bulbs. However, LED lights may perform just as well or better. Researchers recently conducted a study to determine the effect of different cannabis lighting on rooting and vegetative growth in cannabis clones. They used clones of three commercial cannabis strains and tested them under three lighting types:

  1. Blue (400–500 nm), Red (600–700 nm), and Ultraviolet-A (UVA) LED lights (in different combinations)
  2. Phosphor-Converted White LEDs
  3. Fluorescent light

While fluorescent lights are tried and true lighting for plant initiation, LED lights are more energy efficient. Previous research has suggested that LEDs might have some advantages too. Some insights from past studies note that higher proportions of blue light may promote faster rooting of cannabis clones, and the addition of UVA light may increase root biomass and help clones resist transplant shock. Higher proportions of blue light might also encourage a more compact plant morphology.

The lights for this study were all set to a canopy-level PPFD intensity of 200 µmol·m−2·s−1 and a 16-hour photoperiod. After the clones were rooted, some were harvested for evaluation and others were grown for an additional 21 days of vegetative growth under metal halide lamps at a PPFD of about 275 µmol·m−2·s−1. Researchers observed that root index levels were higher for clones grown under LEDs with enhanced blue light and UVA versus fluorescent light. The dry weight of roots was also higher for this type of lighting, but fluorescent lighting performed better than white LED light. Clones that were grown under LED light with an enhanced blue spectrum also had thicker stems than those under LEDs with blue and red or white light. Overall, clones grown under fluorescent light had the least amount of vegetative growth at the end of the study. The results suggest that LED cannabis grow lights with enhanced blue and UVA spectra perform slightly better than fluorescent lights for cannabis clones and juvenile plant growth.

References

Moher, M., Llewellyn, D., Golem, S., Foley, E., Dinka, S., Jones, M., & Zheng, Y. (2023). Light Spectra Have Minimal Effects on Rooting and Vegetative Growth Responses of Clonal Cannabis Cuttings. HortScience, 58(2), 215-221.

https://journals.ashs.org/hortsci/view/journals/hortsci/58/2/article-p215.xml

Sabine Downer
Author: Sabine Downer