Yet at the same time, I was also worried about spending a whole bunch of money on grow equipment since I wasn’t even sure if I could successfully grow.
If you have a Lux Meter to measure your brightness levels, you can get even more accurate with your grow light distance. While a Lux meter isn’t perfect for everything, it works well for measuring light levels under fluorescent, MH and HPS grow lights.
For the sake of ease of use, I recommend getting a ballast that is digital, dimmable, and supports both MH and HPS bulbs.
Example MH/HPS Setups
How To Set Up Your Exhaust
Your bulbs will need to match your ballast. If your ballast supports 600W Metal Halide, you need to get 600W Metal Halide bulbs. If your ballast supports 1000W High Pressure Sodium, you need to get 1000W High Pressure Sodium bulbs.
While this doesn’t affect most indoor growers, if the exhausted air has to move a very long ways after going through your fan before it’s vented outside (for example the air has to go through several feet of ducting after passing through the fan), a bigger exhaust fan might not be enough – you may need booster fans along the way.
I bought a huge sheet of foam and glued (super glue and hot glue for best results) it to a sheet of corrugated plastic. You can buy both these items for a few bucks at a home improvement store like Home Depot.
Quick Guide – Lux Levels for Optimal Cannabis Growth
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!
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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.
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)
After veg and moving to flower, most growers also agree that switching to a light source with more of the red spectrum is better for flowering. The old standard has been to use either CMH or fluorescents in veg and switch to HPS into flower. This is the tried and true lighting recipe for indoor cannabis growers. By far the majority of cannabis produced in North America today is grown in this way. With the onslaught of LED lighting manufacturers jumping into this new “green rush” of opportunities we are seeing this standard lighting recipe being challenged more and more.
Unpacking Existing Information
This is congruent with other findings that some added blue in flower will cause this. But the reason we see these amounts vary is because every strain reacts differently to different spectrums. Keep in mind that the cannabis plant grew in nature all over the world at different longitudes with different spectrums. With all of the variations of cannabis strains in today’s market made from these ancestral plants from all over the world, each will perform differently under different spectrums.
Most of these “new to horticulture” LED manufacturers are making claims that you should be using a full spectrum LED in flower to truly maximize plant terpenes and THC levels. But is this really true? See the graph below comparing what parts of the light spectrum is used for photosynthesis compared to the full spectrum light from the sun.