Wow, a few weeks ago people were ready to burn me at the stake for saying that inverse square law doesn't really apply in grow tents/rooms with reflective walls, that you can't use open space PPFD matrices to indicate PPFD levels in a grow tent, that PPF (minus losses) divided by surface area determines average light density (plus most of the concept of penetration), that people generally use the concept of penetration incorrectly and that reducing the beam angle with a reflector does not increase "penetration" unless at the cost of surface area covered.
Just wanna repeat that what stardustsailor so eloquently stated, that it's not just the quantity of light, but also a measure of how diffuse the light is. In that sense one 800umol isn't the same as another 800umol. In fact greenhouse tests with diffuse screens have shown improved plant production even though these screens absorb some light. But then sunlight is about is non-diffuse as you can get.
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that inverse square law doesn't really apply in grow tents/rooms with reflective walls(...)
Of course it applies ! But it's way complex -even for advanced software/hardware - to exacty calculate
the energy(or power if you prefer ) levels at a " x,y,z" point somewhere inside the tent/room ..
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that you can't use open space PPFD matrices to indicate PPFD levels in a grow tent(...)
Correct ...
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that PPF (minus losses) divided by surface area determines average light density (plus most of the concept of penetration(...)
Well...At what height ? Excuse me ,I meant distance from light source ?
Space has 3 dimensions (that we know of ,at least ..) Surface is the two of them ...
Furthermore ...
Ain't exactly "average density " ...It depends from the space and light source characteristics ....
Inside an intergrating sphere ,yes ,that it would be "average " ....
Inside a grow tent ,ok ,it's an approximation of average ...
And the less the space becomes reflective and diffusive ,the less "average" it becomes ...
Still , I do not understand the concept of penetration ...
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that people generally use the concept of penetration incorrectly and that reducing the beam angle with a reflector does not increase "penetration" unless at the cost of surface area covered.(...)
A reflector / conc. lens does not increase the output flux of a light source .
(Extra energy is needed for that to happen ..)
What they do actually ,is decreasing diffusion .Pretty useful when the distance of light source from leaf canopy increases and/or there are not any reflective surroundings ...That's why I do trust that those (lenses & reflectors )
mainly find their use in large grow installations (where even in case of reflective surroundings affect only the plants near them ) or in artificial greenhouse lighting ...And yes ,it is always at cost of surface area covered.You gain here ,you lose there ...
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In that sense one 800umol isn't the same as another 800umol (...)
A red laser can have 800umol/sec ,as a HPS bulb ,as also a LED COB light ,as any other light source ...
But ,yeah ...There are some differences among them ...In what way those 800umol/sec are "delivered" to a leaf canopy ....A laser will saturate an area of a top leaf ,and lots of photons will be transmitted to an area of the next leaf under the top one ....Lots of " penetration " ,eh ? But only to a small tiny area ...You get the picture...
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In fact greenhouse tests with diffuse screens have shown improved plant production even though these screens absorb some light(...)
Indeed,in greenhouses diffuse sunlight has shown to increase yields in comparison to direct sunlight .
Diffusing screens used in greenhouses ,are there to " SPREAD OUT " the light
( opposite action of reflectors / concentrating lenses ) in order to be " omnidirectional " so all the plants inside
the greenhouse will absorb ,reflect and transmit light about equally,per plant .
Analogous to using more LEDs/COBs in a given space ,driven lower .
( Not exactly ,but close enough,to get the principle idea .)
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