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Using Light Efficiently
- Thread starter DrPhoton
- Start date
strainsgrow
New member
Great write up Dan. Happy 420! 😥
Campesino
Banned
Thanks DANGERDAN !
SO, why do LED manufacturers all seem to suggest lower heights above canopy during flowering? Is this just to protect very young plants?
I don't have any light meters, so I more or less follow their guidelines. I run 21" above during Veg and at least 15" during flower. They do fine at 15" but I think I saw evidence that they don't like 14". So, does this mean that I can lower them closer to 15" in late veg?
SO, why do LED manufacturers all seem to suggest lower heights above canopy during flowering? Is this just to protect very young plants?
I don't have any light meters, so I more or less follow their guidelines. I run 21" above during Veg and at least 15" during flower. They do fine at 15" but I think I saw evidence that they don't like 14". So, does this mean that I can lower them closer to 15" in late veg?
DrPhoton
New member
Good question. I couldnt tell you exactly why. That would have to be clarified by the manufacturers. However it could be for the same reasons some manufacturers think plants dont use green light, they have a weak understanding in plant and light science. Over the last few weeks i have actually looked at all the best grow light technologies for urban and commercial applications. While also looking at the science the manufacturers provide. I cannot express enough the amount of unscientific and inaccurate data some of them provide. I feel like intellectually vomitting. If i could. This seems to be a common trend and is worse with manufacturers that provide the cheaper products. Some of the better ones like fluence, have some top level science. Which is quite rare. But they are heavily focussed in the commercial industry which typically requires or is best having the level of authenticity that such a large industry would demand.
Perhaps there are valid reasons such as for improved penetration or that they anticipate its safer having lower light intensity during veg and then pushing to the ideal intensity during flower when the plant is more healthy. Or they anticipate the average grower might not know to fill the entire canopy so having the light closer may benefit for any potential wasted light through radiated losses. Who knows.
All i know is that after many months of reading books, one in particular, entirely dedicated to photosynthesis. Also reading all the major papers relating to plant science and photosynthesis. That plants do not have different photosynthetic characteristics during different stages of growth. If they did this would imply that plants change leaf anatomy over the course of their life. Which is just not the case. Even if it was, you would not have to put the light closer to benefit from this. The anatomical changes that would improve light harvesting and utilization efficiency would improve with the same lighting conditions. The only valid reason one could suggest to bring a light source closer would be for concerns of radiated losses or improved canopy penetration (quality reasons only not quantity).
Without a meter its difficult to quantify where the best height will be, this makes the manufacturers recommended specifications the only reliable data outside of actual experimentation. Saying that, staying within the confines of 500-700umol. This level of intensity can be tolerated in both main vegetative growth and flowering. Its possible that flowering plants can tolerate higher intensities, likely because of less DLI from the lower light cycle. Also the extended dark cycle gives more time for repairing photosystem machinery which are damaged during the light cycle. This however does at all not mean you are providing more light to plants. Remember light sources have a finite output capacity which ultimately dictate the photosynthetic potential. You cannot make a lower output capacity light source perform like a higher output capacity by placing it closer to plants. Light inside a vacumme has no resistance, so it travels infinitely unless acted on by another force. Our atmosphere does have some resistance, but the level of light degradation over the distances we are talking about are insignificant. Sub 1 percent.
I hope that answers your question, if not ask away. Sorry for the long response
Perhaps there are valid reasons such as for improved penetration or that they anticipate its safer having lower light intensity during veg and then pushing to the ideal intensity during flower when the plant is more healthy. Or they anticipate the average grower might not know to fill the entire canopy so having the light closer may benefit for any potential wasted light through radiated losses. Who knows.
All i know is that after many months of reading books, one in particular, entirely dedicated to photosynthesis. Also reading all the major papers relating to plant science and photosynthesis. That plants do not have different photosynthetic characteristics during different stages of growth. If they did this would imply that plants change leaf anatomy over the course of their life. Which is just not the case. Even if it was, you would not have to put the light closer to benefit from this. The anatomical changes that would improve light harvesting and utilization efficiency would improve with the same lighting conditions. The only valid reason one could suggest to bring a light source closer would be for concerns of radiated losses or improved canopy penetration (quality reasons only not quantity).
Without a meter its difficult to quantify where the best height will be, this makes the manufacturers recommended specifications the only reliable data outside of actual experimentation. Saying that, staying within the confines of 500-700umol. This level of intensity can be tolerated in both main vegetative growth and flowering. Its possible that flowering plants can tolerate higher intensities, likely because of less DLI from the lower light cycle. Also the extended dark cycle gives more time for repairing photosystem machinery which are damaged during the light cycle. This however does at all not mean you are providing more light to plants. Remember light sources have a finite output capacity which ultimately dictate the photosynthetic potential. You cannot make a lower output capacity light source perform like a higher output capacity by placing it closer to plants. Light inside a vacumme has no resistance, so it travels infinitely unless acted on by another force. Our atmosphere does have some resistance, but the level of light degradation over the distances we are talking about are insignificant. Sub 1 percent.
I hope that answers your question, if not ask away. Sorry for the long response
Campesino
Banned
Thanks DANGERDAN
OK, the info they provide:
24" = 420 umol
18" = 690
12" = 1235
They suggest 24" in Veg, but I keep them 21" (use CFLs for early life)
They suggest 15-18" in flower, but don't provide a 15" reading and it is not linear (Maybe 15" = 910ish?)
At this point I am stuck at 15" for flowering because my plants had more ambition than I expected and the LEDs are already only 5" clear from the top of the tent.
So any serious issues here? Should 18" be my target flowering distance in the future? Other thoughts?
OK, the info they provide:
24" = 420 umol
18" = 690
12" = 1235
They suggest 24" in Veg, but I keep them 21" (use CFLs for early life)
They suggest 15-18" in flower, but don't provide a 15" reading and it is not linear (Maybe 15" = 910ish?)
At this point I am stuck at 15" for flowering because my plants had more ambition than I expected and the LEDs are already only 5" clear from the top of the tent.
So any serious issues here? Should 18" be my target flowering distance in the future? Other thoughts?
DrPhoton
New member
Yea i would say 15" is around 900umols.
Ideally you want to match your plants to your light source as you cannot control the intensity. But because most are limited on how they can do this, you may have to bring your light source closer in order to utilize some otherwise wasted light. When you bring the light closer, and the inner hotspots increase. Much of this extra light goes unused, as you reach the limit of photosynthetic efficiency. But the light on the outer edges increases and does get utilized. So there most definitely is a benefit for bringing a light source closer when the canopy is not completely filled. As a rough guide, you dont want the inner hotspots to be any higher than 1000umols or 80,000 lux. 12" is around 1200umols which is fine if your plant can tolerate it. If however you can back your light off to get between 500-700umol then you maximize the efficiency of light utilization. But the canopy must be filled so most of the light is being received by leaves.
Ideally you want to match your plants to your light source as you cannot control the intensity. But because most are limited on how they can do this, you may have to bring your light source closer in order to utilize some otherwise wasted light. When you bring the light closer, and the inner hotspots increase. Much of this extra light goes unused, as you reach the limit of photosynthetic efficiency. But the light on the outer edges increases and does get utilized. So there most definitely is a benefit for bringing a light source closer when the canopy is not completely filled. As a rough guide, you dont want the inner hotspots to be any higher than 1000umols or 80,000 lux. 12" is around 1200umols which is fine if your plant can tolerate it. If however you can back your light off to get between 500-700umol then you maximize the efficiency of light utilization. But the canopy must be filled so most of the light is being received by leaves.
Last edited:
Campesino
Banned
OK, Thanks.
So, I'll go with 900 @15", because that seems to conform to everything. Plants that got closer than that seemed to start light burn (@<14" probably above 1000umol)
My canopy is certainly full, but the lights really can't go higher so I'll have to stay up around 900umol on several tops
So, I'll go with 900 @15", because that seems to conform to everything. Plants that got closer than that seemed to start light burn (@<14" probably above 1000umol)
My canopy is certainly full, but the lights really can't go higher so I'll have to stay up around 900umol on several tops