Hello.
From the info that I have gathered while researching light and how its used by plants I can say I do know a quite a bit. However I wouldnt dare call myself an expert.... Not yet at least. hehe. First, we are going to start off with the basics. I think we all know that light is needed throughout the entire lifespan of cannabis (at least I hope I think that most of us here are interested in getting the most massive, dense, stinky bud we can while trying to stay cost efficient. (I feel like not enough people take cost into effect when giving their responses and opinions, and seeing how this is pretty much the main reasons we are all asking these questions, you would think people would think before posting simple high priced solutions. " Do two or 3 $30, 150w hps lights accomplish as much as a 250w or 400w HPS (costing usually minimum $100-$150)? UUUUUUGGGG JUST GO BUY A 600W HPS $300.... <---- Not a helpful response, if i had money to drop on a nice new hps ballast, then I probably wouldnt be asking if $30 lights would work, Thank you haha).
Anyway... Most of us also can agree that the specific kinds of light (wavelengths in nanometers-nm and specific colors-red,blue,green..., color temperature in degrees Kelvin-K) needed at the different stages of development are also widely accepted. Knowing the wavelengths of light needed for both vegetation stage and flowering is one of the many keys to a successful grow. Cannabis like other plants uses primarily blue light (apprx 450nm, or 5500-6000k) with little red during vegetation, and red light (apprx 650nm, or 2200K) with little blue during the flowering stage. Now that we know the kinds of light needed, lets discuss the light sources that will create these ever so important wavelengths. First, lets discuss cfls, though they are sufficient and even preferred in many cases for veg, they are not optimal during the flowering stages due to the lack of "intensity." While I have always been told (and constantly see in posts) that more light equals bigger yeild and thicker, denser buds. This brings me to my main question... What is "more light"?
The general unit of measurement you are going to see advertised by light bulb companies are called Lumens. Lumens, in short, measure the amount of light seen by the human eye. As you can imagine, this isnt the best way, or even a good way to measure light for plants. Why you ask?...We "see" or use in the plants case, light differently than what the plant uses for photosynthesis. The human eye is much more sensitive to some colors of light (different colors are caused by different wavelengths of light, red= apprx 650 nm, blue=apprx 450nm), primarily yellow. Plants dont even use the green light viewed by us. This is how plants get there green color, because they are reflecting the unused green light . For example... We now know plants dont use green light, they use or absorb blue and red light predominantly. This means that any light source giving off green light, yellow light remember because the human eye is more sensitive to yellow light (though plants do absorb little yellow/orange light for photosynthesis) or any other color not being absorbed by the plant, is still represented in the "total lumen output" on the light package. So when a light bulb claims to have a certain amount of lumens, only a small percent is actually being used by the plant. This is also why you may see multiple cfl bulbs of the same wattage but with different Kelvin temperatures (another way of representing light, 2200k=red light for budding, 5500k=blue light for veg) with names like "soft while "or" cool blue,"have quite a big descrepancy in total lumens.
PAR is a much more effective way of measuring light because basically, (without all the scientific lingo) it measures the amount of light actually useful to the plant (as I said, red and blue light predominantly). As for " adding light," from what I have read you cannot technically add lumens or PAR (basically you cannot increase the intensity of the light by adding wattage). Which does make sense if you think about it. Two 250w hps lights will not be giving your plants twice the intensity, just twice the light. However the one thing that I havn't really seen people talk about is photons. Don't get me wrong, I am no scientist. I have taken a few chem, bio, cell bio courses for my major but i no way am I an expert. Anyway... photons. Photons are the individual "particles" of light that are given off by lamp or any other source of light. Plants use the light energy (photons) and convert it into chemical energy through chlorophyll via photosysthesis (Im sure we all remember this from elementary school).So this got me thinking... We do know that neither lumens or PAR can be "added" together to form higher intensity light. My theory is that plants even when flowering may not necessarily need this increased intensity, but just more photons. This is where I need to do some more research but my thoughts are that though PAR cannot be added, photons seem like they should. I dont see how adding 2 lights closely together wouldnt increase the amount of total photons absorbed and/or present. Like I said I am no expert. Increased intensity in light may increase the amount of photons in a given space leading to larger and denser buds, but I dont know. I havent really come across any posts explaining the million dollar question... WHY DOES INCREASE IN LIGHT INTENSITY LEAD TO LARGER DENSER BUDS???? or is it even the "Intensity" that causes this? or What technically is light intensity?
