forgive my outburst here, out of nowhere, but I wanted to return to this early post because the subject comes up over and over again, which is better - higher or low current and whether to use optics, and what gives better penetration. Robin answers that pretty definitively. To paraphrase Robin and to add my own BS: the direction of the light is important. It's not magical. Light travels in a straight line unless it's lensed or reflected. High PPF is possible from cobs running softly (current comparison is two cobs at 700mA vs one cob at 1400mA), but for canna it often becomes important to focus the light toward the canopy, instead of it radiating in shallow angles to the canopy, especially if you have more cobs running softly. Depending on what you are growing, and what canopy depth you have to manage, and what PPFD your plants need, you might be well off with unfocused emitters of various intensity and/or distance from the canopy, or perhaps lenses would be best for your scenario. It depends on what you are trying to achieve.
Currently, as of 10/2016, the citizen cluo-1212 cobs are cheap at about $12. Compared to the CXB3590, the 1212 at 700mA/25W is about the same 50% efficiency as one CXB3590 at 1400mA/50W. Two 1212 per square foot would roughly compare to one CXB per square foot, with more diffusion. Running 700mA with the right lense the cobs could be mounted close to the canopy without stressing the plants but have good directional penetration.
The Ledil Stella HB lenses, which give the most rich focus, are currently $22/ea which SOUNDS high. But, for comparison, one 1212 at $10 plus one $6.50 mechatronix heatsink plus one $22 lense, equals a total of $38, less than the cost of one bare CXB3590 cob. One CXB3590 at $45 plus one beefy $15 heatsink plus one $22 lense equals a total of $82.
Two 1212's so equipped at 25W would have about the same power and PPFD, and lower price, than one CXB3590 at 50W so equipped. And the 700mA cobs could be run closer to the canopy while still having good penetration.
In addition, the design of the Stella HB lense might perfectly complement the 36V/700mA power band, which 25W TDP would run cool and bright on the cheap 33W heatsinks
https://led.cdiweb.com/ProductDetail/MODULEDMICRO8650B-MechaTronix/574036/
I'm guessing the thirty-two 1212's at 700mA covering a 4'x4' might be the DIY sweet spot for maximum point source distribution with good directional focus for penetrating the canopy at about 1000PPFD at about 12", and you get more color temps to fool with if you like to mix and match a 5700K in with your 3000K, etc. and the fixtures should run cool and last a long time.
That would seem to make this ~$1800 DIY fixture an interesting alternative to Fluence Bioengineering products, which is what I'd compare it to, rather than comparing to a Gavita. But the price for the DIY is approaching the Fluence product.
But at this point I'd recommend DIY'er wait for the Vero 7 series anyway, that claim up to 210 lm/W at 56W, flux that is effectively double HID, per watt. If the price comes in around $30 per Vero 29 gen 7 that will be awesome.
But for now the DE HPS offers the most economical entry price, although there are heat and power requirements that add cost pretty quickly. Still it's hard for some people to plan to recover their extra investment sometime next year, it's easier to pay a little more every month. That's why the poor stay poor. Anyway, Phillips better start improving their LEC and HPS bulbs by an order of magnitude, or LED will threaten that business soon enough. Phillips took the 1150W DE HPS bulb from 2000µmol to 2100µmol in how many years? Bridgelux offering 210 lm/W over the last generation's 150 lm/W is an increase of over 25%. Imagine what efficacy we will see from future individual diodes.
Penetration seems to be one of the main advantages of the lens and reflectors. I agree at softer drive currents the COB output is not as intense and would benefit more from optics.
View attachment 3577654
The light from COB has a wide angle. Reflector or lens tightens the beam a little so you get more penetration.
I think that even if you run at 1.4mA, 2.1 or higher watts, you could still benefit from optics.
The reflector or lens may have its losses but may actually help efficiently deliver more photons towards the plants.
View attachment 3577663
Consider this chart from from page 1. Assuming you have 1.4amps cobs spaced apart. The red represents light towards 1 sqft. The blue and red together represent light going at 4sqft.
Any photos going out of 4sqft box are at going too much side ways and are not going to be efficiently delivered towards grow space. For these sideways photons
a) if reflective sides then reflective losses, some photos will be reflected away from plants.
b) If large area of plants then those side photons hit somewhere on top of canopy. So you have high numbers on top of canopy but not as much light penetration.
That 4sqft area would be an angle of 90 degrees. Round to 100 degrees. 50 each side. anything outside +/- 50 on each side highlighted in yellow
View attachment 3577655
For taller plants and during flowering.When those photons in yellow area focused a little, it should give better penetration and better overall light utilization.
Which is essentially what a good optics can do. For example the Angelina Reflector as below.
View attachment 3577674
BTW I culled most of the highest efficacy Vero29 gen 7 models of interest to me, from the Bridgelux DS93 data sheet:
http://www.bridgelux.com/sites/default/files/resource_media/DS93 Vero 29 Array Data Sheet Rev A 20160622.pdf
BXRC-27E10K0-C-7X
----855mA
----66.2V
------------------------------56.6W
------------------------------10026 flux 25C
9541
---------------------------------------------177 lm/W 2700K 80CRI
BXRC-30E10K0-D-7X
181 lm/W
38.3W
1050mA
36.5V
6929 flux at 25C
6751 flux at 85C
BXRC-30E10K0-C-7X 3000K CRI 80
----855mA
----66.2V
---------------------------56.6W
---------------------------10444 flux at 25C
9938 flux at 85C
--------------------------------------------185 lm/W 3000K 80 CRI
BXRC-35E10K0-D-7X
181 lm/W
38.3W
1050mA
36.5V
6929 flux at 25C
6751 flux at 85C
BXRC-35E10K0-C-7X
----855mA
----66.2V
--------------------------56.6W
--------------------------10757 flux AT 25C
10236 flUX AT 85C
-------------------------------------------190 lm/W 3500K 80CRI
BXRC-40E10K0-D-7X
183 lm/W
38.3W
1050mA
36.5V
6996 flux at 25C
6817 flux at 85C
BXRC-40E10K0-C-74
----855mA
----66.2V
-------------------------56.6W
-------------------------10861 flux at 25C
10336 flux at 85C
------------------------------------------192 lm/W 4000K 80CRI
BXRC-50C10K1-D-74
80
200 lm/W
38.3W
1050mA
36.5V
7669 flux at 25C
7472 flux at 85C
BXRC-50E10K1-C-74
80
----855mA
----66.2V
--------------------------56.6W
--------------------------11191 flux at 25C
10650 flux at 85C
------------------------------------------198 lm/W 5000K 80CRI
BXRC-50C10K1-C-74
70
----855mA
----66.2V
--------------------------56.6W
--------------------------11906 flux at 25C
11329 flux at 85C
------------------------------------------210 lm/W 5000K 70CRI
BXRC-57E10K1-D-74
80
191 lm/W
38.3W
1050mA
36.5V
7332 flux at 25C
7144 flux at 85C
BXRC-57E10K1-C-74
----855mA
----66.2V
------------------------56.6W
------------------------11384 flux at 25C
10833 flux at 85C
-----------------------------------------201 lm/W 5700K 80CRI
BXRC-65C10K1-D-74
70
197 lm/W
38.3W
mA 1050
36.5V
7534 flux at 25C
7341 flux at 85C
BXRC-65E10K1-D-74
80
195 lm/W
38.3W
1050mA
36.5V
7467 flux at 25C
7275 flux at 85C
BXRC-65E10K1-C-74
80
----855mA
----66.2V
-----------------------56.6W
-----------------------11593 flux at 25C
11031 flux at 85C
----------------------------------------205 lm/W 6500K 80 CRI