Does high light intensity produce better weed?
Yes it does. Cannabis growth rate and yield increase up to very high light intensity of 1,800 µmols/m²/second.
As the light intensity increases the potency or cannabinoid level will stay the same or increase. Terpene levels increase with higher light intensity improving the quality of the harvested flower.
New evidence that higher light intensity improves the potency and quality of cannabis flower
The reduced heat from LEDs means growers can increase their grow light wattage without worrying about heat build up. Growers can now deliver light intensity 2 or 3 times higher than with old technology such as High Pressure Sodium grow lights.
This increases the yield you can get from a grow space but does increasing light intensity produce higher quality weed?
Scientists have studied the relationship between light intensity and cannabinoid and terpene production. There are two independent studies we reference with conclusive results showing harvest quality improves as light intensity increases.
The links to the scientific papers published in 2024 from the Netherlands and 2021 from Canada are at the bottom of this article.
Both studies included a large number of plants and controlled experiments where the yield, cannabinoid and terpene levels were extensively tested to determine the effect of increased PAR intensity.
Yield increases linearly up to high PAR intensity levels
In both experiments the yield increased relative to PAR intensity up to 1,800 µmols/m²/second. This demonstrates the capacity of Cannabis plants to utilise very high PAR intensity with very little reduction in efficiency.
The first study shows a linear increase in yield from 600 µmols/m²/second to 1,000 µmols/m²/second.
The second study shows the yield increases when PAR intensity is increased up to 1,800 µmols/m²/second. In this study CO2 was elevated at 1,200 p.p.m.
Cannabinoids may increase or stay the same with increased light intensity
In one study Cannabinoid concentration increased significantly with an increase in light intensity, see the graph below.
Cannabis quality increases with light intensity
The smell of cannabis is determined by organic compounds in the flowers called terpenes. There are many types and each one has a different characteristic. For example limonene delivers a 'lemony' smell.
The level of terpenes also effects the quality of high you get. Higher levels of terpenes result in a more fulfilling high.
In both experiments the level of terpenes increased as light intensity increases.
Links to published experiments on light intensity and harvest quality:
Wannida Sae-Tang, Ep Heuvelink, C´eline C.S. Nicole, Elias Kaiser, Kjell Sneeuw,
et al., High light intensity improves yield of specialized metabolites in medicinal
cannabis (Cannabis sativa L.), resulting from both higher inflorescence mass
and concentrations of metabolites, Journal of Applied Research on Medicinal and
Aromatic Plants. Link here: https://www.sciencedirect.com/science/article/pii/S2214786124000561
Victoria Rodriguez-Morrison, David Llewellyn and Youbin Zheng., Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment, Frontiers in plant science. Link here: https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.646020/full
