Maximizing crop yield in large commercial cannabis grows requires a careful balance of lighting strategy.
Regardless of the type of light installed, HPS, MH, LED or florescent, there are three variables to keep in mind when planning your lamp layouts.
Uniformity of light over the target canopy area. Intensity of light on the maturing canopy, and the photosynthetic spectrum of light the lamp produces.
We're fortunate at FGI because we visit hundreds of commercial grows every year. During our visits we're often invited to take measurements of these three variables. What we've learned is the growers who consistently produce the highest dry weight yields, with the most consistent potency are doing a great job managing their grow lighting. We know growers who achieve 4 lbs per lamp and we know growers who get by with 1.5 lbs per lamp. That is a dramatic difference in potential grower revenue.
We've also found that lighting is frequently mismanaged. For example HPS lamps which are installed and eighteen months later are using the same bulbs. Or lamps hung too far apart which create gaps in PAR (photosynthetic light) output. We also frequently see lamps installed too high above the canopy which wastes light as it travels a greater distance to reach the target area.
All of those mismanaged light strategies sacrifice yields because of issues with uniformity. Old HPS bulbs decline in photosynthetic light output. Lamps hung too far apart or too high (or for that matter too close) creates gaps over the target canopy which if not corrected costs the grower dry weight yield which could have been converted to sales.
The easiest way to check uniformity is to use a handheld PAR meter and a tape measure to set an imaginary plane where the canopy will be growing at various stages.
We frequently see people taking PAR or PPF measurements only directly under the light. But it's the areas between a set of lamps that matters. The area between two or more lamps is called a crossover zone. Two light sources crossing over creates more PAR than one lamp alone. But two lights incorrectly spaced creates less PAR in the crossover area than either light is producing directly below the fixture. Fix that problem and you fix the yield problem.
Another way to plan for proper uniformity is to use programs like AGi32 which when used correctly will provide a PAR map across any target area and will correctly project crossover light levels.
At FGI we use AGi32 as a planning tool when we measure a grow room. We'll look at the light below the lamp and also to the sides where crossover issues occur.
We also use AGi32 to target the total PAR we want on target. We know from experience that mature cannabis plants need between 850-1100 micromoles of photosynthetic energy across the entire canopy. If we lose even six inches of PAR around the edges we've left yield on the table.
We can use tools like AGi32 and PAR meters like the Apogee MQ500 to validate uniformity and intensity. Then we can use tools like the Passport mobile spectrophotometer to measure spectrum.
When properly applied we know that a grower has a lighting layout that will maximize their cashflow cycle after cycle.