I would not invest into 40 1212's, but If you like Citizen COB's, here is the CLU048-1818C4353H5 in 3.500k, Ra90 on B.B.L,
for 16,80€ each +VAT = ~400,-€ for twenty COB's. (other spectrums and COB's also available)
And remember this:
20x CLU048-1818=20x 324=6480 LED's vs. 40x CLU048-1212=40x 144=5760 LED's = 12,5% more LED's
and surely more light at the same current...
Where to buy?
http://www.tme.eu/en/details/clu048-1818c4353h5/white-power-leds-cob/citizen/clu048-1818c4-353h5k2/
Its close but its not the same
1818 4000K80Min 20 COBS
@450 mA ON 5.88 PROFILE HEATSINK
16 SQ.FT. CANOPY 92% EFFICIENT DRIVER @10 CENTS PER KWH
Total power watts at the wall:
496.29
Cobs power watts: 456.59
Total voltage forward: 1014.64
Total lumens: 82558.48
Total PAR watts assuming 10% loss: 219.83
Total PPF: 1160.22
PPFD based on canopy area:
780.53
PAR watts per sq.ft.: 13.74
Cob efficiency: 53.50%
Power watts per sq.ft.: 28.54
Voltage forward per cob: 50.73
Lumens per watt: 180.82
Heatsink riser thickness / number of fins / fin's length: 0.27in/14/1.0in
Heatsink area per inch: 260.01 cm^2
Total heat watts: 214.60
umol/s/W: 2.54 LER: 338.00 QER: 4.75
Heatsink length passive cooling @120cm^2/heatwatt: 99 inches
Heatsink length active cooling @40cm^2/heatwatt: 33 inches
COB cost dollar per PAR watt: $2.09
Electric cost
@12/12 in 30 days: $17.87
Electric cost @18/6 in 30 days: $26.80
Cost per cob: $23.0
Heatsink cost per inch cut: $1.74
Total cobs cost: $460.0
Total heatsink passive cooling cost: $172.26
Total heatsink active cooling cost: $57.42
1818 4000K80Min 20 COBS @500 mA ON 5.88 PROFILE HEATSINK
16 SQ.FT. CANOPY 92% EFFICIENT DRIVER @10 CENTS PER KWH
Total power watts at the wall:
553.51
Cobs power watts: 509.23
Total voltage forward: 1018.45
Total lumens: 91428.15
Total PAR watts assuming 10% loss: 243.45
Total PPF: 1284.86
PPFD based on canopy area:
864.38
PAR watts per sq.ft.: 15.22
Cob efficiency: 53.12%
Power watts per sq.ft.: 31.83
Voltage forward per cob: 50.92
Lumens per watt: 179.54
Heatsink riser thickness / number of fins / fin's length: 0.27in/14/1.0in
Heatsink area per inch: 260.01 cm^2
Total heat watts: 239.34
umol/s/W: 2.52 LER: 338.00 QER: 4.75
Heatsink length passive cooling @120cm^2/heatwatt: 110 inches
Heatsink length active cooling @40cm^2/heatwatt: 37 inches
COB cost dollar per PAR watt: $1.89
Electric cost
@12/12 in 30 days: $19.93
Electric cost @18/6 in 30 days: $29.89
Cost per cob: $23.0
Heatsink cost per inch cut: $1.74
Total cobs cost: $460.0
Total heatsink passive cooling cost: $191.40
Total heatsink active cooling cost: $64.38