Using Light Efficiently

[DrPhoton]

Removed for security reasons

[strainsgrow]

Great write up Dan. Happy 420! 😥

[DrPhoton]

I wrote it while i was watching the nba playoffs, had a great day

[Dutchman1]

Always good stuff Dangerdan, thanks.

[DrPhoton]

Thanks dutch.

[Campesino]

Thanks DrPhoton !
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]

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.

[Campesino]

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

[DrPhoton]

Sounds about right,

[DrPhoton]

Updated and changed title name.

[Bluto]

Excellent read and very informative. Thank you.

[DrPhoton]

Improved readibility and added further information.