When it comes to building an ROI comparing eco farm led lights versus HPS be careful with results that are supplied by manufacturers of only one type of light source. I have seen manufacturers on both sides of the argument manipulate numbers to favor their specific light source. Below is an outline of things to look out for when receiving an ROI comparing lighting technologies:
EFFICIENCIES
With LEDs most will use μmol/J (“Micromoles per joule” with joule being a measurement of watts). This is easy math you can do yourself.
To use the PL Light TopLED R/MB as an example: 320W fixture with PPF of 860 μmol is 2.7 μmol/J (860 / 320 = 2.6875) where the 1000W DE HPS has an output of 2100 μmol is 2.1 μmol/J (2100 / 1000 = 2.1). This is important because I have sat in many presentations, by LED manufacturers, who show how quickly they can hit a good ROI with their LED and use 1.85 μmol/j as their HPS comparison. They’re not lying about this but they are using the old single-ended screw in 1000w HPS lamp in the comparison. These lamps have an output of 1850 μmols at 1000w. But, it is an old technology only in use by small hobby grows these days. I have seen manufacturers use as low as 1.7 μmol/J for HPS which would be the equivalent to the end of life of the old HPS technology.
LIGHT PLANNING
When comparing both technologies, always compare light levels of the entire grow and not just fixture to fixture. I cannot stress enough that there is no such thing as a 1-for-1 replacement of HPS by LED! That simply does not exist in the marketplace. Yes, there are LED fixtures that exist when measured directly beneath the fixture. The output looks equal to or even greater than an HPS. But, when you move the PAR sensor any direction from centered beneath the LED the light level decreases much more under the LED than any HPS fixture!
ALWAYS ask for a light plan that shows an average light level in micromoles AND a uniformity average (hopefully above 90% uniformity). Most LEDs are a very directional source of lighting. If a crop is grown under lighting that is not uniform across your canopy but instead has “hot spots” and “dark spots” it will cause you trouble as the hot spots will use more water, evaporate water, absorb nutrients, etc. at a different rate of speed then the dark spots! To truly have an “apples to apples”comparison be sure to compare light plans with the same targeted light level in micromoles and close to the same average uniformity number. If a supplier cannot provide you with these numbers then it may not be someone you should be considering.
HPS or LED: A Key Factor to Consider
One of the reasons you still hear people claiming that indoor soil grow lights is not ready for commercial cannabis grows is because the reflectors from an HPS fixture mounted 4 ft from the canopy will provide a wide angle of light so the crop will receive light from the fixture directly above as well as the lights from the next row over and even 2-3 rows away. This light is coming in from different angles hitting the crop beneath the canopy leaves that are causing shadows from the light above. This does not happen if you are using an LED fixture that is a big panel of full spectrum led grow light or made up of multiple LED bars where they have to be mounted 9-12 inches from the canopy. You get no crossover from the fixtures but only shadowing from the top of the canopy.
It was only after companies like P.L. Light and Philips* introduced LED fixtures specifically engineered for truss mounting in a greenhouse, that growers really adopted this technology. These products enabled even the indoor grower to maintain some distance between the LED fixtures and the plant canopy, and resulted in production similar to growing under HPS. (*In the United States, Philips has taken the stance that they will not support sales into the cannabis industry as it is not recognized to be legal by the federal government)