Forgive me if this info is out there already, but I want to post while it's fresh in my mind. I just received a lux meter in the mail, and am a little surprised but what I've learned about my LED light. I ordered the lux meter based on this recommendation in a thread where I'm fretting about having plants that are somewhat short (but not too bad!) at 4 wks old.
I have a Platinum LED 300p, which is of course a very popular light. This is my first grow and I'm growing 6 plants in a 2.5' deep, 4.5' wide, 5.5' tall cabinet.
I'm surprised by just how rapidly the lux drops off when the meter is slightly outside the width of the light. Here's what I'm seeing...
90,000 -- Outdoor reading. ~93 million miles from the sun, on a hot sunny June day in the early afternoon.
80,000 -- Indoors, 12" below my LED light, dead center beneath the light. Not bad!
19,000 -- 12" below the LED light, right at the corner of the light. If you hung a plumb line from the corner, this is the area right where that line would hang.
8,000 -- 12" below the LED light, an inch or two outside the zone directly below the light. If you hung a plumb line from the corner, this is the approx reading an inch or two inches further outside of that boundary.
So the lux 12" below the center of the light is 10x more intense than the light just an inch or two outside of the "drip line" of the light. Outside this core zone, the reading will actually go up a bit if you raise the light, since there is some light coming down at an angle outside the core zone.
I knew the lenses were engineered to direct light straight down, but I didn't guess they'd be quite so effective.
On the other hand, there seems to be very little correlation between growth of the plants in veg and whether they are positioned directly below the light or somewhat outside the core zone. In fact, I think I now see why my tallest, most proactive plant bends toward the light when I lower it... because the lower the light, the less light falls outside the core zone. Raise the light up a bit, and the plants outside the core just grow straight up... with significant variations from plant to plant that I'm sure have much more to do with genetics than light.
I have moved my plants around at times, so this is all quite unscientific, but I do know that my tallest plant has never lived in the core zone... tho it does reach a hand or two toward that zone.
I'm also now somewhat more confident that some burning I see on a few leaf tips is due to periods of time when I lowered the light down too much, rather than my nutes. A plant will reach toward the light even if this results in burning.
My room has orca film on the walls, FYI, but given how much light drops off outside the core zone, I'd say fretting over the reflectivity of one's walls is overrated. No doubt it's worth adding some reflectivity with paint, plastic or whatever. But I doubt it matters much whether walls are 85% reflective or 95%, etc. I do like my orca film though.
I suspect a 450p would work quite well in my space. The 300p will probably get me some reasonably good results, I suppose. For this grow I'll either add a couple CFLs for flower or I'll order the 450p and sell the 300p... or use the 300p for a separate smaller cabinet. I might also make a small triangular reflector (cardboard + orca film) to hang ~6" below the light and bounce some more the light to the perimeter.
Despite all of the above, I'm not at all sure that position of the plants relative to the light has been a major factor in the growth rate to this point, compared with other factors. Like I said, the tallest plant, by far, has been living outside the core zone and has not bent aggressively toward the core zone except when I lower the light too much. All my plants tend to angle their solar panels roughly perpendicular to the falling light, most of the time.
I have a Platinum LED 300p, which is of course a very popular light. This is my first grow and I'm growing 6 plants in a 2.5' deep, 4.5' wide, 5.5' tall cabinet.
I'm surprised by just how rapidly the lux drops off when the meter is slightly outside the width of the light. Here's what I'm seeing...
90,000 -- Outdoor reading. ~93 million miles from the sun, on a hot sunny June day in the early afternoon.
80,000 -- Indoors, 12" below my LED light, dead center beneath the light. Not bad!
19,000 -- 12" below the LED light, right at the corner of the light. If you hung a plumb line from the corner, this is the area right where that line would hang.
8,000 -- 12" below the LED light, an inch or two outside the zone directly below the light. If you hung a plumb line from the corner, this is the approx reading an inch or two inches further outside of that boundary.
So the lux 12" below the center of the light is 10x more intense than the light just an inch or two outside of the "drip line" of the light. Outside this core zone, the reading will actually go up a bit if you raise the light, since there is some light coming down at an angle outside the core zone.
I knew the lenses were engineered to direct light straight down, but I didn't guess they'd be quite so effective.
On the other hand, there seems to be very little correlation between growth of the plants in veg and whether they are positioned directly below the light or somewhat outside the core zone. In fact, I think I now see why my tallest, most proactive plant bends toward the light when I lower it... because the lower the light, the less light falls outside the core zone. Raise the light up a bit, and the plants outside the core just grow straight up... with significant variations from plant to plant that I'm sure have much more to do with genetics than light.
I have moved my plants around at times, so this is all quite unscientific, but I do know that my tallest plant has never lived in the core zone... tho it does reach a hand or two toward that zone.
I'm also now somewhat more confident that some burning I see on a few leaf tips is due to periods of time when I lowered the light down too much, rather than my nutes. A plant will reach toward the light even if this results in burning.
My room has orca film on the walls, FYI, but given how much light drops off outside the core zone, I'd say fretting over the reflectivity of one's walls is overrated. No doubt it's worth adding some reflectivity with paint, plastic or whatever. But I doubt it matters much whether walls are 85% reflective or 95%, etc. I do like my orca film though.
I suspect a 450p would work quite well in my space. The 300p will probably get me some reasonably good results, I suppose. For this grow I'll either add a couple CFLs for flower or I'll order the 450p and sell the 300p... or use the 300p for a separate smaller cabinet. I might also make a small triangular reflector (cardboard + orca film) to hang ~6" below the light and bounce some more the light to the perimeter.
Despite all of the above, I'm not at all sure that position of the plants relative to the light has been a major factor in the growth rate to this point, compared with other factors. Like I said, the tallest plant, by far, has been living outside the core zone and has not bent aggressively toward the core zone except when I lower the light too much. All my plants tend to angle their solar panels roughly perpendicular to the falling light, most of the time.
