Introduction: Fully Adjustable DIY LED Grow Light and Grow Box - Complete Light and Cabinet Build (all Under £300!)

Hi everyone,

After my several earlier experiments with a small LED grow light and LED algae scrubber, I decided to turn my attention to a much larger project of building a solid indoor grow space and a full scale LED grow light. I had played around with MDF and wooden grow boxes before however I always felt they were obtrusive and the fact they were flammable always played on my mind. Likewise, all the grow tents had used have been so flimsy and again obtrusive that I felt they were really a poor grow box to have around the house.

After looking at the shear cost of professional pre-built grow cabinets, I decided that anyone could build one more cheaply and also improve on the design.

Aside from the obvious lack of solidity of grow tent and flammability of wooden boxes, I also realized that a lot of light was wasted above the light fitting thus increasing the need for LED power and thus adding unnecessary heat.

As I pondered this problem I realised that an adjustable grow space (that changed with the size of the plants) combined with a fully integrated LED light rig would help reduce this loss of light and allow better efficiency. Also, I realised that in building the LED light myself I could integrate an exhaust system that cooled the LED light at the same time as moving air through the space. This would increase efficiency further and allow for an even tighter fit of the light to the top of the grow space. Again, helping with efficiency.

Considering the problems of the pre-made cabinets, grow tents and MDF options I set myself the following brief for the project:

  • Be adjustable so the space could change with the size of the plants.
  • Have an integrated LED growlight.
  • Must be completely self-contained
  • Constructed of metal or another mainly non-flammable materials
  • Not to look obtrusive as an object in the house/garage.
  • Bet completely light sealed
  • Have the electrical parts well away from the plants, water etc.
  • Come in at under £300 for everything (including LED lighting, ventilation and housing). This would be fraction of the cost of a pre-made build and hopefully a better design.

After much consideration, I realised the cheapest and most effective way to create a professional and solid grow cabinet was to buy and retrofit an ordinary metal office filing cabinet, which can be picked up very cheaply second hand from any office clearance places.

The project turned our really well so I thought I would share the design of the cabinet and LED light fitting with you for comment, improvement or just information purposes.

* As with anything I post please note this is for information purposes only. The project involves using power tools and simple electrical wiring. If you decide to be inspired by the project please note you are doing so at your own risk. The writer accepts no responsibility for damage to electrical items, property or people. Take care with any DIY project and when in doubt consult a professional.

Step 1: Parts List - Bill of Materials and UK Sources

As the project was divided into several distinct Sections I have divided the bill of materials up in this was as well.

Filing Cabinet with Removal Shelves (IMPORTANT!) - £0 - £50

Mine was second hand from a local office reclaim place. I have seen them gumtree for free if you can collect.

Make sure you get one that has removable shelves!! It is critical to make changes between the shelves for different parts of the grow box design. DON'T IGNORE THIS!

Ventilation Kit - £90 - £120 depending on upgrades

I used a Primaklima 180/280 MH 2 speed kit from Growland. Its pretty quiet and has two speed adjustments. The kit came with ducting and clips and I upgraded to get the carbon filter and sound baffle ducting as well. I recommend getting as a kits it works out much cheaper to buy all as one. I purposely choose a fan much larger than needed for the grow space as it would allow me to double up its use to cool the LED growlight and make sure no air escaped the box without first passing through the filter. Again you could easily opt for a smaller fan and no filter and it would be much cheaper.

120mm PC Fans - Free - £5

I hacked these from an old PC I found at the dump straight out the power supplies. Totally free.

If you can't find an old PC then will probably be you best for a cheap 120mm fan probably around £5

12v DC Supply
I used an old 12v laptop supply, but you really don't need much to power a few 12v pc fans. Many available at ebay or amazon. There is an example below - again didn't use so can't see if this is a good supplier or not :

180W LED Grow light - £131.37

60 x 3W LEDs with PCB star - £51

(I choose the following 3W Bridgelux models geared towards flowering plants). I used this company before on my other builds and they worked great. Also delivered next day for free and seem to have everything in stock all the time.

30 x Deep Red 800mA (640-660nm)

5 x Bright Red 800mA (620-630nm)

10 x Bright Blue 750mA (460-470nm)

5 x Royal Blue 750mA (440-460nm)

5 x Warm White 750mA (2900-3200k)

5 x full Spectrum (380-740nm)

General page for all the colors is here if you decide my ratios are not great (I know this is a constant source of debate with people in the growing community!)

4 x 600mA 30 – 50v Constant Current LED Drivers - £35.99

To keep Costs down I used some simple switching 600mA drivers. I had used these on other builds and were reliable and cheap. They also came with a 5 year warranty which I could not argue with.

700mm Aluminium Heatsink – £35.99

This fitted the cabinet nicely with plenty of room around it to circulate. I also had enough room to add another one if I felt like doubling up the power. As it happened I didn't need to but you certainly could if you wanted to supercharge the plants.

10m Low Gauge Cable – - £3.39

Cheap low gauge wire for soldering between the LEDs

Thermal Glue OR Compound (you won’t need both) - £5

For placing between backs of the LEDs and the heat sink. If you are lazy use the glue if you want to change the arrangement at a later date, drill and use thermal compound. This is what I did.

DON'T use both together!

Larger 2 core cable - £6.49 (very optional)

For longer cable runs. I could have used the low gauge cable but thought the enclosed 2 core cable was neater.

Mounting System

Metal Cables - Free

Mounting System I built my own using chain I had in the garage (again optional as you could buy a complete mounting system from a hydroponics place for few pounds I just had the gear lying around. to be honest the chain I used was probably too thick so would advise getting a thinner gauge.

8 x M6 Large Eyelet Bolts + bolts - £8

I had a load in the garage but I am sure you can get them cheaply on ebay or Toolstation etc. Links below I did not use but this is the kind of thing. Note you DON'T need to get an expensive marine grade one. Just mild steel is fine.

8 x Carabiners £5

Again already had a load but Toolstation or ebay will be cheap as chips.

Light Sealing - £5

Foam sealing tape - The type used for sealing windows from drafts. Mine was from toolstation but at the time of writing they don't seem to sell it anymore.

This is an example from ebay - again didn't use this so make up you mind about the seller and quality of tape.

Aluminium Duct tape - £5

Mine came with the ventilation kit but can be bought cheaply at Toolstation. Make sure you get the aluminium one and not the plastic one. I ended using this stuff everywhere to patch any little light holes so needs to be completely opaque.

Power Supplies

6 Gang Multi-Plug - £9.99

I used a half decent 6 gang power supply protection to add a little extra peace of mind for the power coming in. Purchase from Amazon. Note with this build all the sockets got used so I would consider a larger one if ever think you will upgrade the light and add more drivers + fans.

6 Amp Terminal Blocks - £2.04

Most will probably have some of these lying around if not I got pack of 10 (packs of 3 are available) pretty cheaply with the LEDs from here:

Total Project Budget with all the additional parts I added is around - £200 - £300 (depending on optional extras). You could significantly reduce this by getting a free cabinet from somewhere and buying the inline fans second hand on ebay, gumtree etc.


Total project time - 3 - 4 days (could be quicker if you have a decent bench top drill or decide to glue rather than drill!).

Step 2: Before You Start - Tools You Will Need

The project is actually pretty light on tools so most people will have some if not all of these in the garage. The only marginally difficult/risky part of the build was drilling the metal. However, a good drilling fluid and 18v hand drill got through the thin mild steel of the cabinet without too much bother.

I usually get all my gear from Toolstation as they tend to be the cheapest in the UK and can usually be picked up same day.

Step 3: Cabinet Design Concept

My concept for the design was simple. I would
effectively have three chambers moving up the cabinet each separated by a movable shelf which would allow the grow chamber to shrink and grow as the plants at the bottom grew. Each shelf would help minimize light loss from the growing chamber thus making it more efficient and needing less LED power.

The three chambers are as follows:

1. Bottom Growing Chamber for light and plants.

2. Middle chamber for hanging the fans which would suck warm air away from the heat sink and exhaust it above.

3. Upper Chamber where the carbon filter would sit and all the electrical components thus keeping them well away from any water when feeding the plants. The hole in the top of the cabinet would act as both entrance for the main power feed and the exhaust vent for the whole cabinet.

Step 4: Lighting Design

The LED grow light was built using 60 x 3W LEDs screw mounted on an aluminum heatsink. The lighting design was based on 4 roughly equal series circuits powered from a separate constant current driver (as per the schematic above).

In addition, each separate circuit had an inline 800mA fuse placed between the driver and the first LED just in case of issues with the circuit. The drivers have circuit protection how for the few pence a fast blow fuse cost it seemed sensible to add this to protect the LEDs and drivers in case of faults with the wiring.

Also just a note on the LEDs, there are many many poor quality LEDs on the market, I highly recommend using decent brand name chips such as the Bridgelux ones on my build. Not all LEDs are made equally despite often looking similar. I have tried many and found the ones I have from to be really good and a really good price.

Step 5: Building the LED Grow Light - Marking Out and Drilling the Heatsink

Having done a few projects involving LEDs I knew this would take some time so I approached this section first.

The first step was to mark out a grid on the heatsink in pencil marking out where the 60 x LED centers would be.

Then measuring a distance of 0.95mm either side of the horizontal center lines I marked out where the centers of the drill holes would be.

Step 6: LED Light - Drilling the Heatsink and Adding Self Tappers

After marking out all the drill holes, I went along and drilled each ones using a 2.5mm drill bit (I got through a few of these so if you are short it is worth buying several as this is pretty laborious task and you will break some if you are using a handrill).

As I went along I double checked each one against the size of an actual LED PCB just to be sure I was drilling in the right place.

I then worked the Self-tapping screws into the metal to create the thread inside the metal. Make sure you use the correct size hole and screw as I snapped one when I did not make the hole large enough.

Once the hole had been threaded I screwed on the non-conductive washers so the whole thing was ready to have the LEDs mounted.

Step 7: Mounting the High Power LEDs

Now the drilling has been completed it is just a case of applying thermal grease to the rear of each LED and screwing them down with the screws and non-conductive washers. This sandwiches the thermal grease between the back of the LED and the heatsink. You want a good layer and there should be some excess coming from the sides when you screw them down.


Step 8: Wiring Up and Testing the Grow Light

Once everything is mounted on the board

I soldered lengths of light gauge cable between each LED. Again, this is a bit time consuming but once it is done I had a cable linking each LED in the circuit to one another (as per the schematic)

I then drilled another hole at the end of the heatsink and attached a 12 gang 6A terminal block. The positive and negative cables form each of the 4 circuits were then terminated into each on side by side.

Once this was done I wired some flex and a UK plug to each of the drivers, then connected some more flex between the low voltage outputs of the driver and the terminal blocks. I opted to solder on a Pico 800mA fast blow fuse onto the flex, just to protect the LEDs and drivers in case of any future problems in the circuit.

Each circuit was then tested with a driver for functionality. And then finally all together.

Once happy everything was working I put this one side and started working on the cabinet.


Step 9: Sourcing the The Cabinet

In choosing a filing cabinet I realised early on it would be beneficial to buy a white one with white powder coating on the inside to minimise light loss.

Also, my design concept would require the shelves to be moved around so I made sure I found one with removable shelving which conveniently were also white (as pictured). There were a few standard sizes to choose from. I opted for H180 x B80 x D39cm, which appears to be quite standard. However, there were lots of options for a wider and much higher units depending on your space requirements. Given I was only looking at few small plants I did not see the benefit but other might if they are looking to grow some monster trees.

Step 10: Drilling the Cabinet and Shelving Holes

First main job was to drill the cabinet and shelving with 4 large holes using an 18v hand drill 120mm and 80mm hole saw and some cutting oil.


I cut the holes in sequence top to bottom as follows:

1. 80mm hole in the top of the cabinet.My power supply came in form the right at the back and I wanted the carbon filter on the right so I placed it here.

2. 120mm hole in the top shelf - make sure you measure the carbon filter to make sure the hole you drill allows the filter to sit comfortably on the shelf with good airflow all around it

3. 120mm in the center of the middle shelf

4. 120mm in the rear of the cabinet in the grow chamber. I then glued a 120mm fan grill over the front which included a filter to catch dust and prevent insects entering


In terms of the process of drilling, this is not that hard but needs a lot of care and precautions.

The steps I took were as follows:




3. Drill small pilot hole with Metal Drill bit

4. Swap drill bit for the hole saw

5. Spray Cutting Oil onto the surface of metal

6. Set you drill to torque setting and a slow speed

7. Slowly push the hole saw into the surface of the metal stopping from time to time to reapply the cutting oil.

8. After a few minutes of light pushing you will get through to the other side without to much bother.

9. File down edges afterwards.

For information, I learnt this from a YouTube video by ultimatehandyman. He uses a much thicker piece of metal than the side of the cabinet but goes into good detail about how to do it and gives some good tips on keeping things safe and tidy. Well worth watching.

Step 11: Adding Eyebolts

Happily, the shelves that came with convenient holes already made in the corners. If this is not the case you would need to drill 4 x M6 holes in the shelves using a metal drill bit.

Once you have done this, simply bolt in 1 of the M6 eyebolts at each corner, using an adjustable spanner to tighten the bolts.

Step 12: Hanging the Inline Fan and LED Lighting

With the eyebolts in place it was simple a case of cutting the chain I had to length and attaching the carabiners to the ends and clipping them onto the eye bolts

Luckily the Primaklimat Fan I had, came with a wall bracket, so after attaching the carabiners was just a case of clipping them on the screw holes in the bracket. In my experience most inline fans have some bracketry to wall mount of suspend them but probably worth checking if you are ever buying one as its key to keep the fan noise down and allow for easy adjustment of the chambers I had created.

Next I had to drill 4 further M6 holes in the corners of the heatsink, then I could do the same with the lighting rig. It is worth getting the measurements all the same in the corners for the drill holes as then the heatsink will hang level much more easily. If not then you will need to play around with the carabiners and cables to get it all looking good.

Step 13: Routing the Ducting

With fan position sorted I removed the fan from the unit and attached the ducting to either side using the clips that came with the set. I then sealed the joins with the aluminum duct tape and tested.

I then rehung the fan and placed the Carbon filter in position. Then it was just a case of routing the ducting into the low shelf and up the higher shelf. I then connected the Carbon filter from the underside of the shelf with the remaining clips and then sealed again with aluminum duct tape.

Step 14: Wiring It All Up

Attaching the Drivers

With everything hanging, all the drivers were then placed on the top shelf. Then all the cables were routed from the drivers and reconnected to the light. Likewise, the plug from the fan was also routed to the top shelf.

Hanging the PC Fan

Next, I took one of the PC fans and hung it with wire from the cables holding the light unit. This free hanging fan would blow lightly across the tops of the plants and as it was free hanging was pretty much silent. I then solder the fan cables to the cables of the 12 v DC supply and placed this supply on the top shelf as well. In larger set ups (or if I has more than a few plants) I would have used more PC fans for air-circulation, however given how large the extractor was for this space I didn't thin it was needed.

Routing the Cables

All the cables were routed through the recess behind the doors and then up to the top. This kept everything in place and didn’t need any mechanical fixing.

Switch ON!

Finally, with everything connected I placed the multi-plug on the top shelf and routed the cable through the hole in the top of the cabinet. Then switch on.


Step 15: Light Sealing

The final step of the project was to seal the light coming out of the box.

Applying Compression Tape

This was done by applying compression tape along every point of contact that the doors made with the main cabinet and the doors. On its own this was pretty effective however in some places I needed to double up the tape to feel the gaps.

Plugging the Gaps with Duct Tape and Silicone

Whilst about 90% of the holes sealed this was I also found a few places I could not reach with foam tape so used aluminium tape and even a bit of silicone glue I had left from another project to plug them. If I had silicone on a gun a probably would have used that as I could have fired loads into awkward places and plugged them really well.

This is definitely the messiest bit of the project but as I took care with the foam seal on the door well the final little spots of light coming through are easy to get rid of.

Step 16: Soak Testing

After completing the project, I ran several days’ worth of tests checking the temperature of the heatsink and temperature of the grow space throughout the day.

Happily, it sat at a steady 24 - 27 degrees during the day and about 5 degrees cooler at night with the lights on. The temperature of the heatsink stay cooled to touch with the inline fan drawing air through it. However, at a later point I decided to add another PC fan that sat on the heatsink in case of the inline fan failing. I wired this in parallel to the other fan from the same 12v DC supply. That way the heatsink could stay cool enough temporarily without damaging the LEDs. A grow box should be checked daily so in the case of a fan failure I had enough cooling capacity to keep everything going without any damage happening.

I should point out the garage I have this running in does not very cold (lowest 15 degrees) as it is behind a closed door. If you are following this or creating a grow box generally you really need to consider the drop-in temp as well as regulating the heat when the lights are off. In a normal garage, the temp drop would not be acceptable and would damage stress or even worse hermaphrodite your plants. DONT FORGET THIS!

Step 17: Conclusion

Once the testing had been done I brought in 4 small plants and grow them very happily through full flowering. The light sealing worked well and the larger inline fan meant no air escaped from the box without first passing through the carbon filter.

Moving the shelving as the plants got bigger worked surprisingly well, although isn't as easy as I hoped. This is certainly something I would look at in the future to improve.

Likewise I might add a further bank of LEDs to switch between vegetative and flowering one day. Would be easy to do and make everything that little bit slicker.

Anyway, hope this is of some interest or use to someone! Would welcome any feedback good or bad to improve on the design and happy to answer any questions if something is unclear.

Thanks for reading!