Growing Marijuana in a Greenhouse: A Detailed Lighting Guide
Accounting for Sunlight in the Greenhouse
>>>In the chart above, all the yellow dots represent days where there’s enough sunlight outside of your greenhouse to hit your yield targets.
>>>But these graphs don’t account for any light obstruction from your greenhouse. There are several greenhouse factors that reduce the light your crops receive, including:
Glazing transmission rates (varies from 92% for single pane glass to 76% for double polyethylene film.)
Trusses and struts
> Thermal curtains
> Fans
>Light fixtures
> Other infrastructure that produces shadows
>>>On top of all these factors, your glazing will never be perfectly clean.
>>>Typically, only 50-65% of solar light outside of a greenhouse actually reaches your crop! For this reason, many more days require supplemental light within a greenhouse than outside.
So How Much Light Do I Need in My Greenhouse?
>>>To keep from losing $14,000,000 per acre in revenue, you decide to purchase LED fixtures to supplement light in your greenhouse. But how much supplemental light should you provide?
>>>An intensity of 150 µmol·m-2·s-1 would increase the days your crop achieves the 40 DLI target to 26%, 300 µmol·m-2·s-1 to 47%, and 450 µmol·m-2·s-1 to 67%. To achieve the 40 DLI target on all days would require 870 µmol·m-2·s-1. This is a decision you must make carefully to find a perfect balance between increased yields and capital expenses.
>>> As you achieve the 40 mol DLI target on more and more days, you will also increase annual gross revenue (Figure 8). With just 150 µmol·m-2·s-1 of supplemental light, revenue increases by $5.3 million USD.
>>>This increase continues with greater supplemental intensities with a maximum gain of $13.7 million USD up to the 40 mol DLI target every day of the year. (Keep in mind that gains well above $13.7 million are easily possible when lighting above a 40 DLI target).
>>>Note that just a 50 µmol·m-2·s-1 intensity increase means at least a million dollars of greater net revenue per acre up to an intensity of 600 µmol·m-2·s-1 .There is an economic threshold at which adding more light does not increase net revenue. At this point, the quantity of light requires a large number of fixtures, so many fixtures that the capital expense exceeds the value of increased yield. In the Arizona example, this economic threshold is 750 µmol·m-2·s-1. This means that the best ROI will be found around 500-550 µmol·m-2·s-1. Other lower light regions will have a significantly higher threshold.
Marijuana Greenhouse Economics Summary
>>>Let’s Review. Cannabis is likely the most valuable crop on a per acre basis. This means very small yield improvements can greatly increase revenue.
>>>Even in the sunny state of Arizona, for each day a grower supplements solar light to achieve 40 mol·m-2·s-1, they will on average increase gross revenue by ≈ $41,000 USD. This adds up to a revenue increase of $13.7 million per acre per year.
>>>In lower light regions, this light-to-revenue effect will be much more dramatic. >>>To ensure these revenue increases are realized, cannabis growers must only use reliable supplemental lighting sources that are proven to grow commercial cannabis, they must supply adequate CO2, and optimize all environmental variables for LEDs.
>>>As earth’s climate changes, efficiency has become more and more important both to sustain the planet and maximize a grower’s net revenue. So it’s time to roll up our sleeves, and provide the perfect light to maximize yield of your cannabis crop. After all, there really is a lot of green on the line.