Anyone who has ever researched marijuana growing will be aware of the need for plants to be exposed to light. Obviously, this isn’t much of an issue if you grow outdoors in a suitable climate. Indoor growers know that they need to expose their weed to a minimum of 18 hours of light per day in the seedling and vegetative stages.
Once you force your crop into the flowering stage, your plants should receive 12 hours of continuous darkness and 12 hours of continuous light each day. What some growers don’t realize is that light intensity is key to bigger yields. Assuming your plants have no major illnesses or infestations, the single biggest factor affecting yield is light intensity.
DID YOU KNOW: The single biggest factor affecting yield is light intensity?
Remember, light is the food of your plants because they turn it into energy via photosynthesis. Too many growers ignore light intensity during the flowering stage, even though this is precisely what drives the production of buds.
Marijuana lighting is big business now, and you can purchase LED, CFL, MH, HPS and many other types of grow lights. Even though we know the importance of light intensity, it is not a topic that has engendered a great deal of research; at least not until recent times. However, we have finally been provided with data from relevant studies, and it is fascinating.
How Does Light Intensity Impact Plant Weight & Bud Yield?
In 2018, OutCo and Fluence Bioengineering combined forces to research the effect of light intensity on marijuana growth. OutCo grows weed, while Fluence designs and manufactures LED lighting applications for large horticulture operations. Fluence claims that its systems provide increased yields, better quality weed, and a reduction in energy bills for their consumers.
Together, the two firms developed a protocol and experimented with the effect of five light intensities on the Hazy OG strain. Before we proceed, it is important to explain a couple of terms to help you better understand the findings of the study.
PPFD | This stands for Photosynthetic Photon Flux Density and is measured in micromoles per second (μmol/s). It quantifies the photons falling on the plant. Along with Photosynthetically Active Radiation (PAR), PPFD is used to determine the usable wavelengths and spectrums of light. Most LED lighting systems use PPFD and PAR to market their potential.
DLI | This term stands for Daily Light Integral and is the number of photons received during any 24-hour period in a single location. As you probably know, your marijuana plants need photons for photosynthesis and for it to occur, your plants must be exposed to between 400 and 700 nanometers of light.
More accurately, DLI relates to the amount of light that reaches a square meter of space, or 10.8 square feet if you prefer. DLI is measured using this formula: moles of light (MOL) per square meter (m) each day (d).
In any case, the study involved exposing the marijuana plants to the following light intensities: 400, 600, 700, 800, and 1200 (μmol/m2/s). Here is what the full table looks like:
- 400: 3 mol/m2/d
- 600: 9 mol
- 700: 9 mol
- 800: 6 mol
- 1200: 8 mol
As expected, the study showed that the weight of trimmed flower and shoots increased linearly with light intensity. The largest rise in production occurred between 400 and 600 μmol/m2/s where trimmed flower weight increased by an incredible 51% while fresh shoot weight grew by 26%.
| Simply put, the study showed that the weight of both flowers and shoots increased with light intensity.
The increases grew far more slowly between 800 and 1200 μmol/m2/s with a trimmed flower weight increase of just 9% and a fresh shoot weight rise of 5%. This data seems to suggest that 12000 μmol/m2/s could be the light saturation point of cannabis. In other words, it may not be worth your while wasting money on more powerful lighting.
What was interesting was the lack of cannabinoid increase with light intensity. The two companies found that LED lighting provided a 12% higher rate of cannabinoids than HPS lighting, however.
Overall, the lighting fixture that provided 800 PPFD offered the best bang for your buck with a 13.5% increase in yield on the 700 PPFD producing HPS system, and it also used 44% less energy.
Other Studies Suggest Similar “Hacks” for Growing Bigger Buds (And Getting Bigger Yields)
Another study, this time by the Laval University in Canada, and published in January 2019, seemed to back up the earlier data. The information it provided could change the way people grow cannabis indoors forever. Standard practice involves giving plants between 300 and 750 μmol/m2/s using HPS or specialized LED lights. However, the Laval team found that you could enjoy greater yields with an easier and more cost-effective setup.
It is assumed that marijuana yield will increase linearly right up to 1500 μmol/m2/s although the 2018 study seemed to suggest that 1200 μmol/m2/s was the likely saturation point. In any case, it is possible to hit 1500 by using broad-spectrum lighting that costs far less than what you would expect to spend. Overall, this type of lighting provides double the intensity of a typical 1060-Watt HPS light.
The study involved members of the Greenseal Cannabis Company who grew hundreds of marijuana plants and ensured conditions such as soil composition and temperature remained constant. The pertinent change was the exposure to types of light and the intensity of the light. Overall, the yield per plant increased by 0.41 grams on average for every μmol/m2/s that reached it.
| DIY cannabis growing hack for producing bigger buds and higher yields? Get better lights!
For example, when a plant was exposed to HPS light of around 500 μmol/m2/s, the harvest was slightly less than 300 grams. When the light intensity was bumped up to 1500 μmol/m2/s using an LED light, the yield per plant increased to a sensational 800 grams.
Of course, the big question is whether the increase in energy costs justifies the increase in yield. The answer here is an emphatic ‘yes,’ although the researchers used a few assumptions. For instance, they said electricity costs $0.11 per kilowatt hour (KWH) while .41 grams has a retail value of approximately $2.32; a figure that changes depending on the strain. In essence, however, your energy bill only increases by $0.04 for every $2.32 of cannabis produced.
The Laval team pointed out that the study was focused solely on yield sizes. As a result, specialized lighting could improve a strain’s cannabinoid profile and justify a price hike, but the study showed no evidence that changing light spectrum bumps up your yield.
Final Thoughts on Grow Hacks for Bigger Yields
Although the data only comes from a couple of studies, it essentially confirms what most growers have suspected all along: that light intensity plays an enormous role in bud size and yield. Depending on who you believe, it is best to keep the intensity in the 1200 to 1500 μmol/m2/s range for best results. What the studies don’t show is how light affects every single aspect of cultivating marijuana.
Even so, OutCo saw enough from the 2018 study to make significant changes to its entire facility; using LED lighting only. The company also announced that it would be adding ‘double stacked’ benches, a change that could provide a 150% increase in square footage. If a major marijuana grower such as OutCo is determined to change the way it does things, perhaps it is a good idea for home cultivators to follow suit and benefit from higher yields.