Kelvins refer to the warmth and color of the light being emitted. During the vegetative stage, cannabis thrives best when provided cool daytime blue light with approximately 6,400 kelvins. Conversely, flowering cannabis performs best with a warmer red light of 2,700 kelvins.
That is why it is a good idea to assess the lumen measurement when considering lights for growing weed. Cannabis plants need lights that provide enough lumens intensity for their proper growth.
For all types of cannabis, it is usually a good idea to purchase lighting that has both blue and red light spectrums. With regular plants, it saves you from the hassles and costs associated with changing the lighting to induce flowering. LED lights have a full spectrum of light, so you can use the same lights from seedling to harvest.
In countries like Canada, where the federal government has legalized recreational cannabis, there is the ability to do more research. The University of Guelph is one organization that is leading the way in this research. As he states in this article from HortiDaily — Michael Dixon, Director of Environmental Control Research at Guelph says: “We have found that the optimal LED spectral recipe changes with every strain of cannabis.” This is a very important statement for growers to consider! Will you be growing just one strain in your grow the entire time? If not, what spectrum do you choose? Yet if the added blue light in flower only increases your THC levels by 4% is there a justifiable ROI in the cost of the added light spectrum?? If so, can you do that by just adding a few MH lamps? Or does the ROI make sense to go all LED? (1000w DE MH lamps are now available with the PL Light NXT 1000w DE fixtures).
Does this article answer our very first question? Let’s break it down and see. Upon further investigation, the crops in question were grown entirely under each light source. Not in a veg room under one type of light and then moved to flower. For this reason, the HPS plants stretched in veg and were not off to a healthy start!
No manufacturer , supplier, or customer can state they know the optimum LED recipe for cannabis (or tomato’s, or cucumbers, or orchids, etc.) as nobody has tested and tried multiple, different spectrums with each one being tuned to a specific strain or cultivar of each plant type to be able to render a quantifiable opinion.
Do this math with your LEDs as well. The PL Light TopLED is 320 watts so the BTUs will be 1092 BTUs. While that looks like a big savings it will take at least two times the amount of our LEDs to get to the same light level as a 1000w HPS. On the other side of this argument is that the LED fixtures do not provide the radiant heat as HPS and your crop roots will perform better with warmth. It is proven that there is a direct correlation between heat and crop production. Plants grow slower, producing less fruit the colder they are. In northern climates many growers rely on the heat from HPS to warm their crops.
The bottom line that I can share with you, from my perspective where I get visibility to lots of opinions on the topic, see lots of sales and growth cycles, talk to lots of growers, is this: We are still in the investigative and development stage with LED technology in this sector.
For this reason alone, this research should be thrown out.
With all of these factors above, how do we answer our initial questions?? Quite frankly, there is no simple answer! Every grow is different – from different: strains being grown, growing climates by geography, style of growers, indoor versus greenhouse, etc. All of these factors will weigh heavy on what is better for you!