This time I drive both row together using off the self constant current source LED driver
LED driver manufacturing spec:
- Input voltage: AC 85-265V
- Output voltage: DC 28-45V
- Output current: 670mA
The result is quite good, brighter than 2x36W PL light, more LED mean brightness more uniform and all the plant produce bubble 30 minutes after light on. I do not have equipment to measure brightness nor PAR, so I wonder if I put too much light but never mind, will see how it goes.
Initially I was worry about the heat generated by LED. In the previous design there are only 3 LED on the 5x60 cm aluminum plate, now its double and it is not a heat sink just a plate without fins. Temperature measured just right under the LED heat sink show maximum 49.7 degree C. Not sure the Juction temperature though.
My guess probably because the LED driven at 670mA instead of 1A. I did current measurement using Tektronix current Probe and LeCroy scope, it show that maximum current is ~897mA, minimum current is ~589mA and average around ~720mA. Voltage measured at the driver output is 36.75V. Thus the LED took around 26W.
Power used by the whole light set (LED + Driver) is around 27W. LED alone take 26W, thus LED driver efficiency is not that bad, only 1W power loss.