Wow, there is no comparison between Cree vs ebay cheap LEDs. Cree CXA3070 is one of the cutting-edge white LEDs at this moment. Compared to ebay COB LEDs, CXA3070 is putting out about 60% more light per watt!!! Most of us are happy with whatever we have been using until we see the difference since we don't know what's out there. There are quite a lot of people who is using artificial light in this forum. So I thought this info may be useful. This is an update to my previous post in another forum. OK, here is the punch line. CXA3070 is $40+$2.23 for holder, and 100W ebay LED is $8. So Cree is 5 times more expensive initially. But after running it 1.04 years, Cree becomes cheaper (I'm using $0.19497/kWh, which is probably higher than most of you). So it doesn't make sense to get the cheap LEDs. I started this thread with the cheap ebay LED. But now, I would recommend Cree CXA3070 over ebay LED. It's difficult to compare against florescent light (or red+blue type LED grow light). But I'm guessing that this CXA3070 is one of the most cost effective ways to grow with artificial lighting. The total costs is about $60 per 50W module of CXA3070 (pretty comparable initial cost to T5HO). You can drive it at a higher wattage (e.g. 100W), but I didn't want to push it to the maximum capacity. Materials LED: Cree CXA3070-0000-000N-Z230F ($40 from digi-key) + LED Holder: TE Connectivity 2-2154857-2 ($2.23 from digi-key) vs LED: ebay "100W" Warm White (similar to the one posted in the begining of this thread, but it has 100 diodes instead of 30 diodes for 30W). $8+free shipping from China CXA3070 (3000K) comes in 3 grades (bins) depending on the efficiency: Z4 (most efficient), Z2, Y4 (least efficient). Mine is the middle bin (Z2). The LED holder is a bit tedious to use (drill holes to the heatsink), but you don't have to solder/glue the LED. Here is the CXA3070 + holder: Comparison of the size: Clockwise from top left: Cree CXA-3070 (3000K, middle bin; Z2), ebay "100W" Warm White (around 3000K), ebay "100W" Cool White (around 6000K), ebay "30W" Warm White (around 3000K) Drivers: I had 3 kinds of constant current drivers, all from ebay: From top to bottom: 50W (1.5A), 30W (1.05A), 20W (0.6A). Heatsinks: whatever CPU heatsink with a fan. From Left to Right: Cree CXA3070, 3000K, ebay "100W" Warm White, ebay "100W" Daylight White, ebay "30W" Warm White. Wire: Cerrowire 18-2 Thermostat Wire (18 gauge, 210-1002BR from HomeDepot). Thermal paste: Arctic Silver Ceramique 2 Measurement: Explanation of the data columns: "fc.1ft": I placed a light meter 12" away from the emitter, aligned to the center of the emitter. It was measured after running it for a minute or more (to stabilize the temperature). "input.W": watt used by LED + driver. This was measured by kill-a-watt meter. "Vf": forward voltage, the voltage across the + and - or the LED (unit: V) "current.A": current going through the LED (unit: A) "LED.W": watt used by LED (excluding driver). This is Vf * current.A Drvr.Effic: Driver efficiency. (=LED.W/input.W) fc.per.inW: footcandle at 12" per given input watt (=fc.1ft/input.W) fc.per.LEDW: footcandle at 12" per given input watt (exclude power loss due to driver) (=fc.1ft/LED.W) Code: LED Driver fc.1ft input.W Vf current.A LED.W Drvr.Effic fc.per.inW fc.per.LEDW CXA3070 20W(0.6A) 520 19.0 33.58 0.469 15.75 0.829 27.4 33.0 CXA3070 30W(1.05A) 970 33.8 35.04 0.864 30.27 0.896 28.7 32.0 CXA3070 50W(1.5A) 1500 59.0 37.03 1.427 52.84 0.896 25.4 28.4 ebay-100W 20W(0.6A) 320 18.8 27.51 0.552 15.19 0.808 17.0 21.1 ebay-100W 30W(1.05A) 480 27.2 28.06 0.866 24.30 0.893 17.6 19.8 ebay-100W 50W(1.5A) 730 46.0 28.81 1.425 41.05 0.892 15.9 17.8 ebay-30W 30W(1.05A) 520 30.1 31.01 0.866 26.85 0.892 17.3 19.4 LED on the left, and lightmeter on thr right: Results (graphical representation): Notes: With regard to the driver efficiency, those cheap ebay drivers (30W and 50W) are pretty good (89% efficiency). But the 20W driver is not great (around 82%). When you look at fc.perLEDW, you notice that efficiency of Cree and ebay LED increases with lower current. I think some other people calculated that radiant efficacy of this Cree can be >40% with 20W (0.6A) driver. In other words, 40% of electic enegy can be converted to light energy (the rest is wasted as heat). However, running Cree CXA3070 at lower current is a false economy. You can run 2x CXA3070 @50W, or 3x CXA3070 @30W to get the similar amount of light. But it takes 10.7 years to make the cost (initial + electricity) even (13h/day). So I'm going to run it with 50W driver As mentioned earlier, after 1.04 years (13h/day), Cree CXA3070 becomes cheaper than ebay LED. I was a bit surprised, that luminous efficiency of the 30W ebay LED isn't so different from 100W ebay LED. These measurements are approximate. For example, the color spectra could be slightly different even though both Cree and ebay LEDs are warm white (around 3000K), and I used footcandle instead of PPF of PAR. Additionally, the light spread could be slightly different and 1-point measrement at the center may be misleading (I think the light spread looks similar).