A recently published 2018 study, originating out of Finland, shows that the choice of light may affect the THC concentration in Cannabis plants. The use of energy efficient LED lights might be part of the answer to an increased THC content.
It is known to most of us that plants need sunlight to grow. This is also true for our beloved Cannabis plant. Basically the more sunlight a plant gets the more it grows. However, with modern society and technological progress, new light sources have emerged. Some are even good enough for the use in plant cultivation.
In terms of cultivating the Cannabis plant, two aspects are mainly of concern. That is flower size and cannabinoid content. The bigger the better and the stronger the better, has been the motto.
But with all these different kinds of light bulbs and whatnot, available for cultivators, which is the one that might get you bigger or more potent plants?
A recent 2018 comparative study called The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L.  might shed some light on that question. To sum it up, growing Cannabis, scientist compared the use of high-pressure sodium (HPS) light, commonly found in street lights, to LED lights. Yes, LED lights, as the small energy efficient ones you find in everything from flashlights to blinking kids shoes.
What they found out was that plants which grew under HPS light were taller than the ones that grew under a LED light. On the other side, while the LED plants were shorter, they had a denser growth. However, all in all the HPS plants had a higher dry weight.
To cite the study, as for the concentration of THC, the differences in favor of LED could be as high as 38%:
”HPS had 38% less (9.5%) THC com-
pared to NS1 (15.4%)”
So, for the choice of light source, it all comes down to what a cultivator wants to achieve with a crop. The light composition seems now to be as important as the duration of light the plants get. Some light types give taller plants and some light types give a higher cannabinoid concentration.
Nevertheless, as insightful as that might be, a look at the authors own conclusions in this study shows even more varied applications and effects when it comes down to choosing LEDs over HPSs. ”Manipulation of the spectrum, an advantage of the LED technology, offers better space utilization to support the heating and cooling loads of growing buildings. LED lighting strategies may be applied to improve the energy utilization and carbon footprint of cannabis crop.”
 Magagnini, G., Grassi, G., & Kotiranta, S. (2018). The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L. Medical Cannabis and Cannabinoids, 1(1), 19-27. doi:10.1159/000489030