I want a certain PPFD. What do I need to get there?

thinking about a switch to either COBS or QB.

Grow area: 3x4x8

PPFD goal: 1500

What do I need at the least cost? DIY or pre-built is OK although I think a DIY would be fun to try.

You have the same issue as me. I ideally want 1500 ppfd I just have a larger space but it's hard to work out ppfd without setting up a fixture then measuring it I've found.

So I'm aiming high and just dial it down with pot if it's too high

George2324 said:

You have the same issue as me. I ideally want 1500 ppfd I just have a larger space but it's hard to work out ppfd without setting up a fixture then measuring it I've found.

So I'm aiming high and just dial it down with pot if it's too high

Click to expand...

hopefully some of these LED gurus give some advice on working backwards towards the correct light.

There are plenty of threads where you can find all the information you need regarding ppfd calculations...

Blinky38 said:

There are plenty of threads where you can find all the information you need regarding ppfd calculations...

Click to expand...

so i saw this in a recent thread:

CXB3590CD36V3500K 25 COBS @0.7A ON 5.88 PROFILE HEATSINK
16 SQ.FT. CANOPY 94% EFFICIENT DRIVER @15 CENTS PER KWH
Total power watts at the wall: 609.57
Cobs power watts: 573
Total voltage forward: 818
Total lumens: 118834
Total PAR watts assuming 10% loss: 330
Total PPF: 1534.5

can i assume since my sq ft is 1/4 of this (12 vs 16 sq ft), that i would need 1/4 the COB (about 19 instead of 25) if all else is equal??

and if that is true above, i need 19 cobs at almost 50 bucks each?

plus drivers, sinks?

holy shit.

If you plan to drive them at 700ma, yes. I think you meant 3/4?

Blinky38 said:

If you plan to drive them at 700ma, yes. I think you meant 3/4?

Click to expand...

oops. yep

PPFD is essitilally PPF per area. PPF being total light, then "D" being the area in m2 that you are allocating the light to...or the density of light in said area.
m2=~3.25'x3.25'...3x3=.83m2, 4x4=1.48m2, 5x5=2.3m2

So let's take a 1000w hps system or a comparable led system outputting 1500µmols PPF. That means end of the day you have 1500µmols worth of photons to work with and/or manipulate into certain areas. But doesn't mean you have 1500ppfd on you canopy/grow area.

If we put that into a 1m2...then it would simply be 1500µmols PPFD...1500÷1=1500
But as the area is increased or decreased that density is affected.
In a 3x3(1500÷.83) = ~1807µmols ppfd
In a 4x4(1500÷1.48 ) = ~1014µmols ppfd
In a 5x5 (1500÷2.3) = ~652µmols ppfd

The issue you are going to have, and is causing higher than needed cost, is that 1500µmols ppfd is very excessive and not really within the plants ideal range. Actual is the generally agreed total saturation point where photoinhibition and total shut down happen.
Even in very elevated condition environments(CO2 and hot), 1000ppfd is still the upper production target.

Greengenes707 said:

Even in very elevated condition environments(CO2 and hot), 1000ppfd is still the upper production target.

Click to expand...

I was basing this 1500 off a study that I found recently on Sativas. Conclusion was that 1500 PPFD was optimal for maximum photosynthesis. Adding CO2 of even 700ppm caused photosynthesis to increase by 50%. Optimal temp was determined to be 30C. They also said "dry" conditions were optimal as well.

But thanks for your explanation.

Most of the posts start off with I want to buy X number of Vero 29's at some current and then calculate from that forward.

I'll see if I can find it and post a link. Was an interesting read.

rkymtnman said:

I was basing this 1500 off a study that I found recently on Sativas. Conclusion was that 1500 PPFD was optimal for maximum photosynthesis. Adding CO2 of even 700ppm caused photosynthesis to increase by 50%. Optimal temp was determined to be 30C. They also said "dry" conditions were optimal as well.

But thanks for your explanation.

Most of the posts start off with I want to buy X number of Vero 29's at some current and then calculate from that forward.

Click to expand...

The audience choice seems to be 700-900 ppfd without co2, or up to 1500 ppfd with co2.

Sativas are tropical, they dont prefer dry air in general. Alot of sativas can even survive humidity in flower unlike indicas.

Perhaps instead of increasing PPFD thru higher wattage maybe approach the situation with more COB's at lower wattage. Instead of running 50w/sf, try a target of 25w/sf and double that to 50w/sf at lower umols and higher lumens will allow a higher ppfd with CO2 and just circulating air instead of exhausting air. lower wattage better temp control and the intensity you are looking for.

Example a 5x5 would normally have 24 CXB 3500k, 36v running at 1400ma; 185H-C1400B; for 50w/sf. use a lower rated driver at 700ma;185H-C700B; and double the COB's to 48 at lower wattage but much higher intensity than just running them at 50w each. 25w COB is more intense than a 50w COB. twice as pricey but it will get you that 1500 PPFD you are seeking

VegasWinner said:

Example a 5x5 would normally have 24 CXB 3500k, 36v running at 1400ma; 185H-C1400B; for 50w/sf. use a lower rated driver at 700ma;185H-C700B; and double the COB's to 48 at lower wattage but much higher intensity than just running them at 50w each. 25w COB is more intense than a 50w COB. twice as pricey but it will get you that 1500 PPFD you are seeking

Click to expand...

Dunno why you suggest going with Cree in 2017. There are cheaper options that happen to outperform CXB3590 because they haven't bothered releasing anything but a new bin: CXM22, CLU048-1212-F1, CLU048-1818-F1, Vero 29 Gen 7 to name a few.

On a side note, doubling COBs will add around 10% PPF in most ranges.

TogiX said:

Dunno why you suggest going with Cree in 2017. There are cheaper options that happen to outperform CXB3590 because they haven't bothered releasing anything but a new bin: CXM22, CLU048-1212-F1, CLU048-1818-F1, Vero 29 Gen 7 to name a few.

On a side note, doubling COBs will add around 10% PPF in most ranges.

Click to expand...

They still work great, low power lower amps and deliver. You may pay less up front but the operating costs are higher with more heat, amps, etc. So each person is allowe an opinion, this was asking opinions. Are you the opinion Nazi too.
CXB3590's work great. Just because there is other LED's ut there does not make them better, just newer. newer is not necessarily better. Dunno why you wanna beat me up for my opinion. Wanna do something buy something.

TogiX said:

Dunno why you suggest going with Cree in 2017. There are cheaper options that happen to outperform CXB3590 because they haven't bothered releasing anything but a new bin: CXM22, CLU048-1212-F1, CLU048-1818-F1, Vero 29 Gen 7 to name a few.

On a side note, doubling COBs will add around 10% PPF in most ranges.

Click to expand...

Dont forget the cxb3590 3500K DB over at cutter.

easy answer, Citi or cob calculator. Long answer Use the Luminous 22 at Cobkits for the best light spread option. closest thing I have is the 1818... still deciding on CRI. Thinking the 70 will provide a bit more red but I would rather have less stretch... choices.. Hope you like wiring.


1818 3500K80Min 48 COBS @400 mA ON 4.85 PROFILE HEATSINK
16 SQ.FT. CANOPY 94% EFFICIENT DRIVER @15 CENTS PER KWH
Total power watts at the wall: 991.43
Cobs power watts: 931.94
Total voltage forward: 2329.85
Total lumens: 161191.49
Total PAR watts assuming 10% loss: 433.05
Total PPF: 2314.42
PPFD based on canopy area: 1557.01
PAR watts per sq.ft.: 27.07
Cob efficiency: 51.63%
Power watts per sq.ft.: 58.25
Voltage forward per cob: 48.54
Lumens per watt: 172.96
Heatsink riser thickness / number of fins / fin's length: 0.14in/16/0.66in
Heatsink area per inch: 200.6 cm^2
Total heat watts: 447.33
umol/s/W: 2.48 LER: 335.00 QER: 4.81
Heatsink length passive cooling @120cm^2/heatwatt: 268 inches
Heatsink length active cooling @40cm^2/heatwatt: 89 inches
COB cost dollar per PAR watt: $2.55
Electric cost @12/12 in 30 days: $53.54
Electric cost @18/6 in 30 days: $80.31
Cost per cob: $23.0
Heatsink cost per inch cut: $0.98
Total cobs cost: $1104.0
Total heatsink passive cooling cost: $262.64
Total heatsink active cooling cost: $87.22

1818 3000K70Min 48 COBS @400 mA ON 4.85 PROFILE HEATSINK
16 SQ.FT. CANOPY 94% EFFICIENT DRIVER @15 CENTS PER KWH
Total power watts at the wall: 991.43
Cobs power watts: 931.94
Total voltage forward: 2329.85
Total lumens: 166923.15
Total PAR watts assuming 10% loss: 458.02
Total PPF: 2473.31
PPFD based on canopy area: 1663.91
PAR watts per sq.ft.: 28.63
Cob efficiency: 54.61%
Power watts per sq.ft.: 58.25
Voltage forward per cob: 48.54
Lumens per watt: 179.11
Heatsink riser thickness / number of fins / fin's length: 0.14in/16/0.66in
Heatsink area per inch: 200.6 cm^2
Total heat watts: 419.37
umol/s/W: 2.65 LER: 328.00 QER: 4.86
Heatsink length passive cooling @120cm^2/heatwatt: 251 inches
Heatsink length active cooling @40cm^2/heatwatt: 84 inches
COB cost dollar per PAR watt: $2.41
Electric cost @12/12 in 30 days: $53.54
Electric cost @18/6 in 30 days: $80.31
Cost per cob: $23.0
Heatsink cost per inch cut: $0.98
Total cobs cost: $1104.0
Total heatsink passive cooling cost: $245.98
Total heatsink active cooling cost: $82.32

Are those ppfd calculations on the app actually correct though?

As I'm looking into having 1 per square foot of citizen 1825 at 1800ma and the ppfd and other details just don't seem right on the calculator