Cheap LED Strips : A Viable Alternative

Gpaw’s Light Project

Years ago when I was sourcing my tent and light I had to settle for what I could afford. So I ended up with a Kind LED K3 L600, a fine representative of the ‘blurple family’, pulling 293W out of the wall. Like some things in life, it was a compromise. It would be a good light for a 3 x 3 tent but sub-optimal for a 4 x 4.
Fast forward to spring of this year and I trip over this thread… oh boy, did that stimulate the little grey cells!

A worthy and necessary project is born.

Rough Lux requirements from the ‘interwebs’:

5,000 lux = cloning
10,000 lux = seedlings
25,000 lux = lower end of veg.
40,000 lux = lower end of flower
75,000 lux = light saturation (CO2 required for further benefit)

1 lux = 1 lumen/square meter. A 4’ x 4’ tent is close enough to call it 1 square meter, so we can say in this case, 1 lux = 1 lumen

and other useful trivia:
70 lux = 1umole/m2/sec
1 watt = 3.41 BTU

Design Criteria:

A minimum of 30 Watts per square foot of growing area is the accepted ‘rule of thumb’ so that works out to 480 Watts.

Like many others, I used the Bridgelux BXEB-L1120Z=35E-4000-C-B3. The specs. 27.3 watts, 39 Volts, 0.7 Amps, 4,780 lm. Twenty of them configured in parallel will draw a total of 546 watts at 14 Amps.
Now the neat thing about the Bridgelux (besides the price)is that they can be seriously over-driven (theoretically up to 100%). This is assuming some solid thermal management, like heatsinks & air movement etc.

I wanted the dimmable drivers external to the tent as they produce 10% of the driving power as heat – so about 30 watts each.

The mechanical design had to be simple enough to be built with the minimal of tools. I settled on 1” aluminum angle, 1/8” thick. 20 strips 46.25” long and 2 end pieces 34.25” long. (No worries, a full shopping list of parts later). That works out to 22(ish) pounds of aluminum…

Driver selection was… convoluted… I started with the biggest driver Mean Well makes, a single 600W driver but it turned out that a pair of 320Watt drivers were 15 bucks cheaper & more power – Bonus! This also means that at 100% power I have about 10% overdrive capability, and will be hitting 40 watts per square foot!
Running 2 drivers and all of the strips in parallel has some design impacts such as having to use heavy copper conductors between the drivers and the strips and reducing 10 pairs of driver wires to one pair from the driver for starters. I went with 14 gauge wires between the drivers and the junction box on the light (12 gauge would be a bit better for copper losses but that was getting too expensive). Each LED strip is connected to the junction box with a pair of 22 gauge conductors.

All of this activity required a new meter in order to get comparable data. At the low end you can get a light meter app for your smart phone but this can be very inaccurate and problematic in high light situations. A PAR meter would be a great choice if money isn’t an issue. A lux meter has a sine correction lens and is reasonably priced. It is good choice for A vs B comparisons. I went with a Dr. Meter LX1330B lux meter (54.95CDN, Amazon).

Comparisons:

Kind LED: (measured directly under the centre of the light)

50” above sensor = 9,250 lux
36” above sensor = 15,000 lux
24” above sensor = 29,500 lux
14” above sensor = 62,000 lux

DIY Bridgelux:

(measured directly under the centre of the light)
50” above sensor = 28,000 lux
36” above sensor = 47,800 lux
24” above sensor = 64,400 lux
14” above sensor = 87,000 lux (CO2 territory)

Dimming tests at fixed heights

At 67” above sensor:
10% power = 2,800 lux
50% power = 23,800 lux
100% power = 38,800 lux

At 48” above sensor:
10% power = 2,700 lux
50% power = 17,700 lux
100% power = 28,100 lux

The first thing I noticed was how even the light distribution was across the tent floor
with the new light, impressive!

Temperature measurements after 100% power for 1 Hr.

The component side of the LED strips stabilized at +5C above ambient (ambient = 19C).
The driver stabilized at 31C above ambient. (glad they are not going to be in the tent)

Frame construction and wiring


Ta Da!

Bonus Cable Porn

Cheers
G

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