Something slightly different today.

Since I now live in a TINY flat with no garden, I’m unable to grow any veg outside (and there’s a really long waiting list for local allotments). So I’ve decided to start growing as much veg indoors as possible. However, being the way I am, I’m trying to put as much DIY engineering into it as possible 😀

Rather than just start by growing stuff on a windowsill – which I’ll be doing later on – I’ve decided to create a small LED system to test out growing stuff inside using LEDs.

Grow Lights

I decided on LEDs rather than other growlight systems simply because I can buy high power LEDs very cheap online, and because they allow me to work with low voltages, making things a lot safer (particularly for when the cat decides to jump up on worktops when we aren’t looking!). Also it allows me to incorporate it into my current HA system without having to worry about switching mains voltage (well for now at least).

My current system uses 12 3W LEDs in a 3×4 array as can be seen below.

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The LEDs cost about £4 for 10 and I bought 10 red and 10 blue. Initially, a ratio of 1:1 was used, meaning I have 6 blue LEDs and 6 red LEDs. This worked fine for a while, but I seemed to blow up 2 red LEDs, so I just replaced them with blue LEDs as they were closer to me at the time. So now there’s 4 red and 8 blue LEDs in a 3×4 array.

The boards either side of the LEDs are current controlling buck converter. The blue LEDs are placed into an array with 2 lots of 3 LEDs in series placed in parallel. Not too happy with this setup as I think this caused my red LEDs to blow (when once of the LED leads came loose, too much current went to the other LEDs causing one to blow!).

I’m going to replace that once I obtain a 19v laptop power supply and can have all the LEDs – of the same colour – being powered in series. But that’s for another post…

The buck converters are setup to limit the current at 600mA, instead of the 700mA stated by the seller to try and keep heat down for now. I’m obtaining a thick piece of aluminium which will be better at dissipating the heat, so once that arrives I’ll try and up the current and see if it can still dissipate the heat.


As this is an initial experiment and I’m trying to keep the costs down as much as possible, I’m trying to use as much from around the house as possible.

Below you can see the VERY basic setup that I have at the moment.


As I said, it’s VERY basic!

I simply switch the lights on and off using the wall switch, but soon I’ll incorporate it into my HA system and control the lights via a wireless relay.


I have however, created a simple Openhab page to allow me to easily control the growlights via my HA system. As can be seen below, I – will be able to – control when the growlights come on or off and then forget about it.


However, you can see a temperature chart at the bottom. This was just a small test for me to see if my lettuce would be getting too hot under the lights. For this I just used the wireless temperature sensor that I had in my bedroom and placed it in the growbox. As can be seen, the temperature goes to about 25C when the lights are on and drops to about 20 when the lights are off. For me this seems fine – please let me know if you think these values are too high.

1 week progress

I’ve had the system up and running for about a week now. I’m growing a packet of mixed lettuce as a “cut and come again” method.

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Above you can see the lettuce progress after 1 week. They have started to grow their first true leaves and they aren’t that “leggy” yet. At this stage on a windowsill, I would expected them to be more leggy than this. The seedlings under the blue LEDs seem much happier than those under the red LEDs. I’ll see if that continues.

So far I’m quite happy with the setup and I’ll keep you updated on the progress of the growbox and the lettuce.