DIY Chip-on-board (COB) LEDs
DIY Chip-on-board (COB) LEDs
CXA3070 + TE Holder
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Introduction and COB Advantage
I've posted about other LED lighting options for plant growing. In my opinion, COB LEDs have three advantages: easy assembly, high efficiency, and affordable cost. You can create a highly efficient fixture with individual LEDs, but it generally costs much more than COB-based units. Most DIY LED enthusiasts have migrated to using COB technology. Some grow light makers have also started using this technology. If you prefer pre-made COB grow lights (though you'll need to pay at least twice the DIY cost), the following companies offer COB-based products:
Simple Assembly
COB is a relatively recent technology that packages multiple LEDs into a single lighting board. A 50-100W fixture can be made from a single COB unit. Older DIY LED projects required connecting numerous individual LEDs (e.g., 1-10W each) to achieve a decent amount of light output. Thus, COB LEDs significantly simplify the assembly process, although they require a bit more work than XF-3525L.
High Efficiency
One main advantage of COB LEDs is their ability to handle heat more effectively (with any LEDs, heat is the enemy of efficiency). Efficiency in LEDs is complex and depends on various factors like current and heatsink usage. Driving LEDs at lower currents can increase efficiency. Some designs achieve 70% radiometric efficiency from Cree CXB series.
Affordability
The older method of making DIY-LED panels from individual LEDs can achieve high efficiency but at a higher cost. In contrast, you can assemble a fixture with a single 50W COB LED for $50-80 on average. A 50W COB fixture can illuminate a 2'x2' area for orchids requiring low-medium light.
Here's a list of materials needed, a step-by-step assembly method, and output measurements:
Materials
You basically need six items: LED, constant current driver, CPU heatsink, 18 gauge wires + AC plug, thermal paste (thermal grease, thermal interface material, TIM), and a 5-12V AC/DC adaptor. When looking for parts, cob led manufacturer can be a good resource.
Tools Required
- Drill press (or drill), drill press vise useful but optional.
- M3-0.5mm tap and matching 2.5mm drill bit.
- Methods to connect wires (soldering or connectors).
- Wire stripper.
- Digital multimeter (helpful but optional).
Materials Update (Fall 2016)
Recent products include Bridgelux Vero 29 Gen 7 and Citizen CitiLED CLU048 Version 5. These have varying efficiency and cost but generally outperform older models like the Cree CXB3590.
LED | Driver | Total Lumen | Total Watt | Current per COB (mA) | Vf per COB(V) | Lumen/W | Cost | Comments |
---|---|---|---|---|---|---|---|---|
4x Vero 29-B | HLG-120H-C1400A | 23820 | 135.6 | 700 | 48.4 | 176 | $150 | This should cover 4'x4' area for low-moderate light orchids. Dimmable. |
2x Vero 29-D | LPF-60D-36 | 9754 | 57.8 | 835 | 34.6 | 169 | $80 | This should cover 4'x2' area for low-moderate light orchids. Dimmable. |
2x CLU048-1212C4 | LPC-60-1400 | 8048 | 47.4 | 700 | 33.9 | 169 | $41.5 | This combination may be a bit dark at edges for 4'x2' area. Non-dimmable. |
2x Vero 29-C | LPC-100-700 | 17730 | 90.6 | 700 | 64.7 | 196 | $88 | Intense light for 4'x2' area, good for full sun carnivorous plants. |
Assembly
- Drill holes in the heatsink for the LED holder. Mark positions with a punch.
- Use a small drill press to make accurate holes. A vise can help hold the heatsink.
- Tape the holes to make threads for M3 screws.
- Attach the COB LED holder with short M3 screws. Make the thermal grease layer as thin as possible.
- Connect the wires to the LED holder, paying attention to the polarity (+ and -).
- Connect the LED wires to the constant current driver, ensuring correct polarity.
- Connect the AC side of the driver to an AC plug, matching the color codes.
For AC/DC adapter connection to the CPU fan, cut off the plugs and connect the corresponding wires. The tricky part is drilling and tapping the heatsink. Here, I have 4 of them covering a 120x120cm area.
Measurement Method
I measured several COB LEDs driven at different currents. The relevant quantity is the photosynthetic photon flux density (PPFD). PPFD counts the number of photons between 400-700nm, making it more useful than foot-candles/lux.
Full sun in summer gives about 2000 µmol m-2 s-1, approximately 10000 foot-candles. I used a digital multimeter to measure the forward voltage (Vf) and DC current through the LED, and calculated energy consumption as Vf * current. Note that this does not include energy loss from AC/DC conversion efficiency, which varies between 80-90%.
Cheap eBay "100W" COBs were also included for comparison:
Clockwise from the top left: Cree CXA-3070 (3000K), eBay "100W" Warm White (3000K), eBay "100W" Cool White (5000K), eBay "30W" Warm White (3000K).
Measurement Results
I plotted PPFD against wattage at 12" distance. Different plot symbols indicate different LEDs, with CXA3070 as squares, Vero 29's as circles, and cheap eBay COBs as 'x'. Colors denote light temperature: red for warm white (3000K), blue for cool white (5000K), and green for in-between (4000K).
- Vero 29 and CXA3070 perform similarly well, but cheap eBay "100W" COBs have very low efficiency. Vero 29 and CXA3070 are about 50% more efficient.
- Efficiency increases with lower current.
- Some cheap eBay drivers have good efficiency (~88%), but others do not (~78-82%).
Note on Inexpensive COBs from eBay
I started with cheap eBay COBs (2x "100W" and 2x "30W"), but these are not worth using despite their low cost. Cree and Bridgelux COBs have about 50% higher efficiency, making them cheaper to operate in the long run.
300W 25A DC12V CV Waterproof IP67 LED Driver
The Color Difference Between Warm White 2700K, 3000K, 4000K, 6000K Pure White, and 7000K Cool White
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(For further reading and specific color temperature details, refer to our additional reading resources linked above.)