Lighting The Way: Justice, Gerovac Investigate LED Use In Growing Cannabis

LED lighting has revolutionized industries across the world and Dr. Allison Justice is here to show that it has a place in the cannabis industry.

Justice runs the cultivation side of OutCo, a Southern California-based cannabis retail, research, and extraction company. She said that throughout her work on cannabis, lighting has continually shown to be a key factor for indoor cultivation, but detailed looks into the various factors has yet to occur.

“I don’t know how many times I’ve been told you can’t grow cannabis under LEDs,” Justice said. “Or that you can’t flower [the plants]. Nobody really had an answer for why. It drove me to develop this program.”


Justice partnered with Josh Gerovac of Fluence Bioengineering for the investigation. Gerovac and Fluence have developed a number of products in the cannabis cultivation area, but focus on LED light technology. The pair presented data from a study on the effect of different light spectrums and quantities on the flowering stage of cannabis sativa at the MJBizCon in Las Vegas in November.

Justice and Gerovac controlled temperature (23.7°C), humidity (52.5%), CO2 (1511 PPM), and soil conditions, and grew clones of a Hazy OG cultivar of cannabis. They used automation for watering and other environmental controls to eliminate human error.

The study looked at a variety of wattage LED lights while directly comparing the 1000-watt LED and 1000-watt high pressure sodium or HPS lights. HPS has long been the standard in the industry for its ease of use, wide availability, and light production; but ceramic light fixtures, double-ended lights, and LED technology have been making inroads into the traditional dominance of HPS lights in cannabis cultivation. All light was measured in photosynthetic photon flux density (PPFD), which is a measure of how much light actually reaches the plant. This proves to be a much more accurate measure than photosynthetically active radiation (PAR) or lumens. The 1000-watt LED produced 1200 PPFD while the HPS fixture produced 700 PPFD, while using approximately the same energy per fixture.

Looking at the results from the plants, the LEDs also seemed superior in many cases. The pound per fixture yields were 2.53 vs 2.01 when comparing the LED and HPS. While HPS and LED had nearly identical terpene yields, plants grown under the LED tested at 20.8% THC while the HPS plants tested at 19%. Gerovac said they didn’t notice any variations in the terpene profiles between plants grown under both types of lights.

Justice and Gerovac didn’t stop the analysis with the botanical information; the pair expanded the information to the economics of cultivation. The pair factored in the higher cost to purchase the LED light fixtures, which is approximately $1,200 more a fixture. Assuming a return of $2,000 a pound for cannabis grown, the gains from yield alone would nearly equal the extra cost for the LED lights. Their study showed an estimated $38,000 higher return on investment from LED over HPS lights. Presumably you could get a higher price for the LED- than HPS-grown product as well, due to the 1.8% difference in THC content of plants grown under them.

Justice and Gerovac found the reduced temperature load of the LED lights also allowed cultivators to keep the fixtures closer to plants. With this improvement, they were able to stack two layers of plants vertically in a building—effectively doubling the cultivation space.

The two cannabis scientists have already begun working on the next round of tests. They plan to use more variables, push for higher light density, and look at how to influence cannabidiol or terpene production.

For more information visit Fluence.Science or OutCo.com.