In this chapter, we build an efficient grow light using LED strips and an aluminum frame, that also serves as a heat sink. Power consumption varies between 180W - 480W depending on the LED driver selection and the number of LED strips used.
Aluminum frame for support and cooling
1000+ SMD LED
Adjustable height
Low height, only 3cm / 1 inch
Or visit the Gbox420 GitHub page and download the entire project.
Out of the possible combinations of LEDs and drivers, I would like to highlight the following four builds that hit the sweet spot for different goals:
Power-efficient: Highest power efficiency, with low light intensity. Optimal for seedlings / clones only. Not really suited for flowering or large plants.
Cost-efficient: Bringing the most out of a budget, can bring a plant from seedling to full maturity
Ideal: This is the optimal choice for a two plant grow tent (60x60cm / 24x24"base)
High output: Optimal for large grow tents (120x60cm / 48x24"base)
In this guide, I'm going to build the Power-efficient and Cost-efficient versions of the lights. Below is the spacing difference between the 8 strips/ 1400mA and 14 strips/ 700mA versions. There is a noticeable airflow reduction with the high strip count version, this configuration is not really recommended with an overhead fan.
As the driver is a heat source it is best to keep it away from the plants by mounting it outside the grow area. Optionally the LED driver can be fitted on top of the frame.
The cost-effective version will utilize a 240W - 1400mA (HLG-240H-C1400A) internally adjustable driver. At 1400mA the forward voltage of one strip is 20.5V, making the total required voltage 164V for 8 strips, this is within the supported 89 - 179V range.
Internally adjustable(A): Under the rubber cap in the bottom right corner it has a built-in potentiometer for adjusting the light intensity with a screwdriver. This is done by changing the current the driver provides between 30 and 100%. The water resistance rating is lower due to the extra opening (IP65 ).
The power-efficient build will have a 185W - 700mA (HLG-185H-C700B) externally adjustable constant current driver. The forward voltage of one LED strip at 700mA current is 19.5 V making the total required voltage for 14 strips 273 V, this voltage is within the 143 - 286 V supported range of the driver.
Externally adjustable(B): Notice the extra cable coming out from the driver’s top right side used for dimming the lights. That has to be connected to a 100k Ohm linear potentiometer or a PWM signal source. It has a higher waterproof rating: IP67 and a wider range of dimming: 15% to 100%.
When to get an externally adjustable B version:
If you plan to use the Arduino-based monitoring and controlling system.
If access to the driver is limited or hard to reach. In this case, you can route the potentiometer of an externally adjustable driver to a more accessible location.
Planning to use dimming a lot. The internal adjuster can wear out and it is difficult to replace.
185W, 700mA, Externally adj: Amazon.com
185W, 700mA, Internally adj: Amazon.com
240W, 1400mA, Internally adj: Amazon.com
320W, 1400mA, Externally adj: Amazon.com, Amazon.com, Amazon.de
320W, 1400mA, Internally adj: Amazon.com, Amazon.de
480W, 1400mA, Extern adj: Amazon.de
480W, 1400mA, Int+Extern adj: Amazon.com
Converting an internally adjustable driver into an externally adjustable is easy using a nail, a tire air valve cap, and some grease. You will also need to use glue, a metal saw, and a rasp. This method is only recommended if the brightness is adjusted rarely to avoid wearing out the internal potentiometer.
Poke a nail through the cap of the adjuster hole and glue a tire valve cap on the nail's head
Cut the entire length to 40 mm / 1.57 inch
Flatten the edge of the nail using a rasp
Apply a little grease on the nail and insert it back into the driver
Counterclockwise: Decrease brightness, Clockwise: Increase brightness
With externally adjustable drivers dimming can be achieved the easiest by connecting a 100kΩ (kilo Ohm) linear potentiometer between the dimmer cables. Setting the resistance to 100kΩ or above will output maximum power, dialing back on the resistance dims the lights. Do not use the dimmer to turn off the light completely by setting the potentiometer to 0Ω as the dimming circuit is not designed for that. To protect from accidental over-dimming it is best to have a 10kΩ resistor in series with the potentiometer, this limits the lowest dimming to 10%. If you would like to explore the other dimming options or would like to dim your light completely, please refer to the HLG manual here.
Wiring
The potentiometer and a resistor need to be connected in series between the two dimmer cables. As the dimmer cables are interchangeable the only thing we need to get right is the potentiometer wiring. Connect the center leg to one of the dimmer cables, and one of the side legs to the resistor. Depending on which side leg you choose, the dimming will happen clockwise or counterclockwise, in this example turning the dial clockwise will increase brightness. To avoid damaging the driver by over dimming a 10kΩ resistor is connected in series with the potentiometer.
10kΩ resistor inline with the 100kΩ potentiometer
10kΩ resistor soldered in series, shrink tube will be added over it
Euro style wire connector added to ease attaching the module to the LED driver’s dimmer cables
The frame is made out of 2 mm - 5/64" thick 25 x 25 mm - 1" x 1" L-profile aluminum to match the width of the LED strips. The frame consists of two support rails for hanging the assembly, interconnected by several cross rails to mount the LED strips on.
When calculating the size of the frame the minimum width is equal to the LED strip length plus two times the L-profile width. Depth is limited by the grow box depth and depends on the number of LED strips and the spacing between them. To allow airflow through the lights leave at least a strip's distance in between the cross rails.
Minimum cross rail width using 25mm wide L profile aluminium:
560mm - 22" strips: 610mm /24"
1120mm - 44" strips: 1170mm / 48"
Bridgelux EB Gen2 LED strips
Power efficient build: 14 strips, 560 mm / 22"Cost efficient build: 8 strips, 560 mm / 22"Ideal build: 11 strips , 560 mm / 22"High output build: 8 strips, 1120mm / 44"When sizing the support rails my goal was to use the full depth of the grow box and have the largest possible gap between the LED strips. This allows air from the internal fan to pass between the cross rails and reach the plants under. As aluminum is a soft material the rails can be cut using a hack saw.
The light assembly will be mounted using 5 mm - 3/16" thick carabiners. In preparation for that we need to drill 6 mm - 1/4" holes on the support rails near the corners. Place the four holes close to the top of the rail, so that the carabiner can clip into the hole. Leave a rail's distance from the edges as the screw that will hold down the cross bar on the edge can get in the way of the carabiner.
Hole placed close to the top
Keep a rail's distance for the hole
Mounted light assembly
If the LED driver will be mounted at the center of the frame extra holes will be needed on two cross rails directly under the driver's two opposite mounting points. The hole should be at the center of the cross rail, on the opposite side of the led strip. I have used a 3 mm drill bit and 2mm thick zip ties. This step is optional as it is more recommended to place the driver outside the grow area for better cooling.
If the LED driver will be mounted outside the grow box the DC power input cable needs to be secured to the frame. For this drill two 3mm diameter holes at the center of the support bar next to each other, 5mm from the top. The two holes will be used to secure the DC power cable to the frame using zip ties.
First, we will build the edge of the frame from two support rails and two cross rails. The support rails are at the bottom holding the cross rails up, closing a 90-degree angle. When the aluminum rails are in position and the frame is square mark the 4 drill points at the corners. Use a 4mm drill head for the M4 screws.
Squaring up the frame
Mark the 4mm drill points
Once the hole is ready place a screw in, loosely tighten the nut, and move on to the next corner. When all corners are ready, double-check the 90-degree angles at the corners and tighten all screws.
Now the rest of the cross rails need to be positioned equally spaced between the support rails. If you have N number of support rails, that creates N-1 gaps. To calculate the gap size use: N x profile width + (N-1) x gap size = support bar length. If the driver will be mounted on the top of the frame do not forget to correctly position the special rails with the driver mounting holes.
Example using 500mm long support rails with a 25 mm profile width:
Power-efficient build (14 strips): 14 x 25 + (14 -1) x G = 500 , where G stands for gap size. Solved for G the ideal distance is 11.54 mm.
Cost-efficient build (8 strips): 8 x 25 + (8-1) x G = 500. Solved for G the ideal distance is 42.85mm.
It's easy to see the cost efficient frame will allow a larger air volume to pass between the gaps that can be beneficial in cooling the lights and improving the evaporation from the plants below the light.
Once all cross rails are in place and the frame is ready it is time to mount the LED strips using thermal adhesive. For this, you need to decide on the layout of the different color temperature strips. You can mix and match any color temperature strips, try to aim for a uniform, symmetrical spread of the different colors. I organized my LED strips into three 3500K color temperature blocks with one 5000K strip in between the blocks.
Power-efficient light with 12 x 3500K and 2 x 5000K strips
Cost-efficient light with 6 x 3500K and 2 x 5000K strips
Color difference of the Power-efficient light
The color difference is more visible with the photo out of focus
Using heat-conducting permanent glue is the easiest solution for mounting the LED strips on the frame, just keep in mind that it will be difficult to remove the strips afterward without damaging them.
Before applying the thermal glue make sure both the aluminum and the LED strip surfaces are clean, free of any dirt or oil by wiping them down with isopropyl alcohol. Next, apply a generous and even layer of thermal paste on the back of the LED strip. Do not use too much paste as that would flow out on the sides. Now position the LED strip at the center of a cross bar and place it on the aluminum, use small back and forth movements to push out any air bubbles and form a tight contact between the bar and the strip. Avoid touching the LEDs or getting thermal glue on them, if you do get some glue on the LEDs remove it with isopropyl alcohol and a soft toothbrush. You have about 5 minutes before the glue starts to get thicker, it takes a total of 2 hours for the bond to fully form. If you ever need to remove a strip, try using dental floss.
Note: In some photos, you will see the strips mounted with screws. This was the old way I mounted my strips and it was a horrible job to drill 50+ holes. Since I moved to thermal glue I never looked back.
Rails cleaned using isopropyl alcohol
Layer of thermal glue applied to the LED strip's back
For hanging the assembly I used two eye hook screws threaded into the side of the grow box and two carabiner ratchets with 180 cm / 70" long ropes. One end of the rope is tied to a carabiner using a hangman's noose (Video how to tie a hangman's noose) and the other end is routed through the ratchet. To adjust the height the rope is pulled through the ratchet, shortening the distance between the two carabiners and lifting the lights. The ratchet has a release lever to lower the lights.
Ratchet end of the rope
Hangman's noose on the other end
Carabiner clipped into the support rail
On the DC side, the LED strips are interconnected by AWG 18 / 0.82mm2 solid core wires and the driver is connected using fast release Wago connectors. The connectors on the LED strips support wires between AWG 18 (0.82mm2) and AWG 24 (0.2mm2), try to get the thicker 0.82mm2 / AWG 18 gauge wires as they are easier to push into the connector.
The positive and negative poles of the strips are interconnected with U-shaped pieces of the solid core wire. When cutting the wire measure the distance between two connectors and add 1.5 - 1.5 cm extra on each and strip the first 1 cm of the cable. Then bend the wire into a U shape and push it into the connectors. If you ever need to remove the wires, carefully push a thin finishing nail into the connector and wiggle the wire free.
When using a constant current driver the LED strips are connected in series. The best is to start with the (+) DC cable of your driver and wire it to the (+) pole of the first LED strip. Then link the (-) side of the same strip to the (+) side of the next strip, daisy-chaining all strips using this process. When you get to the last strip in the line, simply connect its (-) side to the (-) DC side of the driver. In the sample build the polarity of the strips change in the middle, this is due to the left side strips are rotated 180 degrees. However, if you follow the wiring the same logic applies: Follow the path from the (+) side of the driver, it always goes from + , - , + , -, + … ending at the (-) side of the driver.
When the driver is mounted outside the grow area the DC power needs to be connected with an extension cable to the light. The connector is made from an AC power extender cable with a C14 and C13 connector.
Chop one of the extender cables in two pieces: Connect the C13 side to the LED driver's DC output. The C14 side will get connected to the LED strips using the Wago connector.
The power connector on the AC side is made from a PC power cable and a waterproof screw locking connector. Choose an AC cable long enough to reach the power outlet even at the lowest light height. I really like waterproof screw connectors as they require no soldering and it is very easy to (dis)assemble them using a single screwdriver. Only work on electric devices after disconnecting them from the power source first!
Simply chop off the C13 connector from the PC power cable, strip back the insulation and match up the color codes of the cable with the LED driver AC input. Inside the connector, there are marks where to connect the different wires: L - Live Brown wire, N - Neutral Blue wire, G - Ground Yellow/Green wire.
The two most noticeable differences of LED strips compared to LED COBs are weight and light uniformity. The assembly is significantly lighter without the additional heat sinks which makes installation and height adjustment easier. For someone who already owns an LED COB lights, it does not make sense to upgrade as the efficiency improvement is marginal. For new starters LED strips are a perfect choice as they are cheap, easy to assemble, light, and very efficient.
