A main factor that must be determined - and might be the most important - is the identification of your end goal when using LED grow lights to grow cannabis. Whether I'm shooting for higher production yields or increased THC, and/or terpene content, I base my light recipes off my end goal.
As we all know, higher quality cannabis, with increased THC and terpene content, doesn't always mean record breaking yields. And a record breaking yield doesn't always mean the most economically feasible solution. An excellent example of these economics can be demonstrated through the HVAC requirements alone. With 1000W HPS lamps requiring approximately 6,000 BTUs of cooling per lamp (depending on room construction and other heat loads) and a 600W LED grow lights producing approximately 2,000 BTUs of heat, it is simple to see that the savings on HVAC alone easily make up for an increase in yield in a larger setup. Not to mention, a direct decrease in energy costs. This is, of course, an equation of revenue per square foot, but the bottom line, with such dramatic operational cost savings, is easy to see.
The cannabis industry has been stuck in a yield based paradigm for decades. But a maturing of the industry has been inevitable as it merges itself with the CEA (Controlled Environments Agriculture) sector, revealing the true cost of an operation. That, and the inevitable enlargement of marijuana grows is placing stress on the environment (and utilities).
Total operating cost per gram may very well be the ultimate metric by which to measure the overall efficiency of a grow operation. But yield is a fairly simple measurement as it does not require an enormous amount of calculation and without stand alone controls and the ability to measure electricity demand in silos of operation, yield is really the only way to measure the productivity.
If that's the bottom line, higher yields can be achieved as well. By providing the plant with the light it needs at the right time of day and life cycle, you will find increased THC, terpenes, and yields. It all comes down to a little tweaking and testing to find what best suits your specific strain.
Has the time come to shed the yield discussion and begin focusing on the overall efficiency of a grow operation - Total Cost Per Gram - as the ultimate grow metric?