So we all know that sunlight is not static. If you are not a botanist, like me, then you tend to rely on correlation. For example, if we see cannabis growing and evolving in high-UV areas – which it does and did – and we know that UV breaks down cannabinoids and we have also read scientific theories that cannabinoids evolved as a way to protect the plants from UV and plant pests, then it might seem obvious that more UV is beneficial.
But the question is, UV spans quite a wide range from around 280nm for UVB to 400nm. So should we give our plants the same ratio as the sun (small amounts of UVB grading to larger amounts of UVA), or is it enough to give them part of that spectrum to get the desired results? And what about the end-grower? Does he or she need to manage that UV by using stronger wavelengths (UVB) with timers to again mimic the sun (UVB is a bell curve that is highest at midday in summer) or is it sufficient to apply a small amount of weaker UV (UVA. near-UV) over a 12-hour period to prevent the risk of UV damage to their plants and make life easier for the grower to manage?
Now let's look at the red spectrum. Should we be providing more red to mimic the sun during autumn when cannabis flowers? Do we recognise that the sun is typically "redder" at the equator where cannabis evolved because the atmosphere is thicker around the equator? Do sativas respond better to red light for this reason compared to indicas which evolved in mountainous regions where the atmosphere is thinner, so there is more blue as well as UV in the spectrum?
Are we going around in circles with the "red for flowering, blue for quality" argument again?
< Joke
As far as I am aware, NASA tried to answer this question with their spectrum tests in the 80s that are still ongoing. The objective was to create the highest yield with the least amount of energy. That meant lots of red light (least amount of energy to produce). But plants did not grow very well under just red light, so blue was added. This was better but as the pants grew, wouldn't it be better to have a bit of light reflecting into the lower canopy? Like green?
This is pretty much what happened, and so the results of at least one NASA test (and I believe there were more, but the link below provides a good start) found a ratio of B=15% G=25% R=60% and a small amount of FR provided the best dry yields.
This is the NASA test and a great comparison of different lighting results on lettuce for anyone interested:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20170010694.pdf
The only issue is this is lettuce, not flowering cannabis – as you have already pointed out Humple. But maybe we could all to point to the leaf areas of those tests and say "Hey, bigger leaf surface area = more photosynthesis = more yield" and that was what the results proved. So shouldn't a plant that produces flowers also be able to use a larger leaf surface area to provide energy for flowering? If that is the case then the photomorphogenic response to red (bigger, thinner leaves, longer stems and petioles that allow light to filter through the whole canopy) would be desired.
Who knows, maybe that is why mother nature also provides more red during flower. Or is it the other way around? That plants simply evolved that way because that's how mother nature works? See, we can still learn a lot from mother nature. That doesn't mean exactly mimicking the sun IMO but using lessons learned from how plants respond to different forms of sunlight at different times of day and year and in different parts of the world to make growing as efficient as possible. I think that's what NASA is also trying to do.
Lol
