The greenhouse method is generally preferred for cannabis growing because, let’s face it, sunlight is free. Cannabis is a demanding crop with high light needs. Growers can’t afford to lose on yields, but it is also important to know how much yield will be gained by adding supplemental light. Let’s look at how far more light will go in a cannabis greenhouse.
The cost to light an acre of greenhouse space at an average supplemental intensity (or PPFD — photosynthetic photon flux density) of 400 μmol·m-2·s-1 is a little under $1M. This may seem like a high cost, yet each additional light fixture a grower provides is like a revenue engine — which can pay itself off in just the first year by increasing flower yields.
At optimal light levels, greenhouse cannabis flower is worth approximately $39M annually per acre. It’s important to note that any light quantity below a daily light integral (DLI) of 40 mol·m-2·d-1 reduces this value. The DLI is a measure of photosynthetically active radiation (PAR) received each day as a function of light intensity and duration.
Horticulturalists generally follow a 1% rule: For most crops, 1% more light means 1% more yield. Cannabis too typically follows this classic rule of thumb; however, there is a point of saturation where the rate of increasing yield diminishes.
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