CobKits
Well-Known Member
thats awesome i cant wait to see their results, ive been out of the loop a bit latelyStephen explained it in a couple other posts. After thermal dissipation, and other things it comes out to an 8-10% increase.
thats awesome i cant wait to see their results, ive been out of the loop a bit latelyStephen explained it in a couple other posts. After thermal dissipation, and other things it comes out to an 8-10% increase.
my par meter at 18" from a 9 cob array n a tent says otherwise, its very uniform.But you should read the post i made with the 2 pictures above... It's a perfect diagram showing why COBs dont penetrate as well as a larger source like qbs/strips.
That's at 18". How's the uniformity at 8"?my par meter at 18" from a 9 cob array n a tent says otherwise, its very uniform.
But they are growing right up close to their STRIPS - which is the strips advantage. They have similar light levels at 18" and below (if running the same wattage and efficacy) but allow growth right up within a few inches of the strips.your case only holds water if people are growing right up to their cobs,
it matters not as theres no plants thereThat's at 18". How's the uniformity at 8"?
again you cant get ideal PAR ("similar light levels") at 18" and at the same time as ideal PAR right up against the strips. if you have 700-1000 PPFD at 18" youd be well over 2000 PPFD right up against the strips - you cant have both, physics is against you.They have similar light levels at 18" and below (if running the same wattage and efficacy) but allow growth right up within a few inches of the strips.
My plants atm are 12" from my 360w qb/fstrip build with no I'll effects.yes thats an advantage of strips, being able to get closer
however being that close to any distributed light source will give you tremendous difference in par once your distance drops
if you are 18" from your light source, going from 18 to 24" (6", 25% farther from the light) gives a much more uniform PAR from top to bottom than going from 3" to 9" (6", 300% farther from the light)
just because you can grow close to a light source doesnt mean you should.
same reason that people who use T5s still keep a distance from the lights, even though you could technically grow right up to them
while i try to keep canopy at teh same distance sometimes it goes wild and ive had colas grow up to 6" directly under a 75W cob to no ill effects
No, the physics is with me - do some ray tracing - and don't forget reflective walls are part of the equation. Its all about overlap and reflection. And 6" or even 3" is not "right up against" the strips. The point is that at 18" you have all of the light sources contributing photons to a given spot. At a 6" distance you have, for the most part, only the diodes that are within a 6" radius contributing to a given point. The closer you get, the fewer diodes are "seen" by a given point. Graying Geek showed this in his measurements. He showed less than a 50% drop in light intensity from 4 inches to 24 inches, if I recall correctly, it went from something like 50k lux to 33k lux..again you cant get ideal PAR ("similar light levels") at 18" and at the same time as ideal PAR right up against the strips. if you have 700-1000 PPFD at 18" youd be well over 2000 PPFD right up against the strips - you cant have both, physics is against you.
That is what conventional wisdom tells us, yes - BUT, you are forgetting that the grow tent is an enclosed, reflective space.the only way to get more uniform par from top of canopy to the bottom is to increase distance of light source from the canopy, so that the ratio of d1 and d2 are as close to 1 as possible (d1=distance from light source to top of canopy, d2=distance from light source to bottom of canopy)like an HID at 36-48", or as a "perfect" example, the sun where d1=93M miles and d2 = (93M miles+8 feet), d1/f2= 1 and allows you to have an 8 foot tall plant with same intensity of light at bottom of plant as the top.
All solid, good info.No, the physics is with me - do some ray tracing - and don't forget reflective walls are part of the equation. Its all about overlap and reflection. And 6" or even 3" is not "right up against" the strips. The point is that at 18" you have all of the light sources contributing photons to a given spot. At a 6" distance you have, for the most part, only the diodes that are within a 6" radius contributing to a given point. The closer you get, the fewer diodes are "seen" by a given point. Graying Geek showed this in his measurements. He showed less than a 50% drop in light intensity from 4 inches to 24 inches, if I recall correctly, it went from something like 50k lux to 33k lux..
OK, follow me on this. One big, bright ass cob at 300W - aside from the efficiency loss, why does no one use that? What's the PPFD at 24" and 48" in a 3x3 reflective tent?
OK, now break that 300W up into four 75W cobs - better right? Ask yourself why. What's the PPFD at 24" and 48" for a 3x3, assuming equal spacing?
Now break that up into twelve 25W cobs - what does that get you? Again what would you see at 24" and 48" in a reflective 3x3?
Assuming equal efficacy of the above scenarios, the total PPF output of each one is the same, correct? so PPFD levels (once you get to uniformity) in the same size tent are going to be the same are they not?
Do you not see that it is simply a mathematical progression towards a theoretical ideal? Strips with lots of diodes is just several more steps down that progression from multiple COBs.
That is what conventional wisdom tells us, yes - BUT, you are forgetting that the grow tent is an enclosed, reflective space.
.
as one aside your breaking 300W cobs into 75W cobs into 25W cobs makes sense but at some points you are in diminishing returns. the difference between 4 cobs and 12 cobs in a 3x3 isnt as apparent as you think there would be little to no difference in average par at 24 and 48". 24" might have a little bit more variation, thats about all. neither strips nor boards are going to magically throw more light deeper in an empty tent. theres still only so many photons to work withGraying Geek showed this in his measurements. He showed less than a 50% drop in light intensity from 4 inches to 24 inches, if I recall correctly, it went from something like 50k lux to 33k lux..
Take readings in the canopy. The PPFD might look good on a flat surface, but in the canopy is where the difference between cobs/qbs/strips becomes very apparent.long read and i feel were on the same team but both taking extreme positions for the sake of argument
but link this id like to see it, and ill respond
ive got a 9-cob rig in a 3x3 tha ti can take some measurements with, an throw some boards in and do the same
as one aside your breaking 300W cobs into 75W cobs into 25W cobs makes sense but at some points you are in diminishing returns the differene between 4 cobs and 12 cobs in a 3x3 isnt as apparent as you think there would be little to no difference in averg par at 24 and 48". 24" might have a little more variation, thats about all
i would say that 9 cob rig (they are about 12" center to center) would give the exact same measurements at 24" as a board/strip rig of equal efficacy
the only advantage is close up uniformity really
I can take readings and compare yours to my 10 strip build at 24". But I already know the outcome lol.i would say that 9 cob rig (they are about 12" center to center) would give the exact same measurements at 24" as a board/strip rig of equal efficacy
to get a true measure of shading and "penetration" ill make some checkerboard shades that take out 10%, 20% etc of the light and measure that way.Take readings in the canopy. The PPFD might look good on a flat surface, but in the canopy is where the difference between cobs/qbs/strips becomes very apparent.
to get a true measure of shading and "penetration" ill make some checkerboard shades that take out 10%, 20% etc of the light and measure that way.
this arbitrary my canopy vs your canopy is useless anecdotal data tbh
will look at your data later
its a little apples vs oranges tho.not sure of how far the cob measurements go, is that 3x3 grid, or are the corners 2" from the side of the 4x4 tent?
i will say that first cob rig measurement at 24" looks fantastic
and ill bet your strips at 24" would look damn near identical
Not my cob build, but yes it is. And I have a grid to put into my 3x3 for PPFD measurements too. But not that many spots lol.i meant the measurements, is that your grid in electrical tape on the bottom?
and if so how can we compare the strips that only measure out to a 3x3 square vs the cob readings all the way to corners of the 4x4? the deep corner measurements will *definitely* lower uniformity
LOL - yeah I do tend to do that sometimes.long read and i feel were on the same team but both taking extreme positions for the sake of argument
If you're referring to Graying Geeks measurements I'll try to dig it upbut link this id like to see it, and ill respond
Yes, exactly - but its the area between 24" and 0" that is primarily affected (by distributing the light source). That zone becomes more homogenous - while the 24" and 48" distances are relatively unaffected, the point at which uniformity is achieved moves upward towards the lights with each reduction.ive got a 9-cob rig in a 3x3 tha ti can take some measurements with, an throw some boards in and do the same
as one aside your breaking 300W cobs into 75W cobs into 25W cobs makes sense but at some points you are in diminishing returns. the difference between 4 cobs and 12 cobs in a 3x3 isnt as apparent as you think there would be little to no difference in average par at 24 and 48". 24" might have a little bit more variation, thats about all. neither strips nor boards are going to magically throw more light deeper in an empty tent. theres still only so many photons to work with
You are correct in that there is a point of diminishing returns. Once you get to less than 6" spacing between light sources, the gains become relatively small. The thing about doing this with COB's is that it gets astronomically expensive to go below one per square foot. Even one per square foot can get pretty pricy. I tend toward favoring strips because they are economical in this regard while still being stupid efficient.i would say that my 9 cob rig (they are about 12" center to center) would give the exact same measurements at 24" and 48" as a board/strip rig of equal efficacy. once your distance of measurement is at or greater than cob spacing the light is uniform and its the exact same principle of overlap/incidental/combined light we are measuring
the only advantage of strips is close up uniformity really (if you are using it). and then when you are stuffing colas in the 6-12" zone below your lights the measurement you took in an empty tent of 'uniform par' 18" down is irrelevant because you just shaded it regardless of how many points of light you have
i mean i get your points but these strips arent some magical unicorn that gives you a perfectly lit canopy 24" deep at uniform levels. otherwise people would be doubling their yields with them on every grow. remember the entire discussion arose when skoomd claimed that cobs were all problematic contrary to the results of almost everybody whos ever used them. yes you can burn a plant by getting it too close to a light. thats HID vs T8 101, but thats grower fundamentals not the lights fault.