Introduction: DIY Plant Grow Light

In this instructable I'll show you how to make your own grow light for indoor gardening!

The light was inspired by what NASA uses to grow lettuce aboard the ISS.

This light is perfect for indoor gardening to make sure your plants get enough light for photosynthesis.

It is made with alternating red and blue LEDs because these are the wavelengths plants use the most. That's actually why plants look green. They absorb all the light in the red and blue spectrum, and reflect the green wavelengths away.

The light is built in modules which makes it easily expandable to any size you need.

This project requires a lot of soldering so it's a perfect project for learning or honing your skills!

If you like this project hit the vote button up in the right corner!

If you want to get fancy with this light add a timer so your light turns on and off automatically!

Step 1: Parts and Tools

Because this project is modular you can make it as big as you need it.

I made my light with four modules, to make the same size as me you are going to need:


  1. 40 red LEDs
  2. 16 blue LEDs
  3. 20 56 ohm resistors
  4. 16 100 ohm resistors
  5. 2 blank circuit boards - 5 x 7 cm
  6. USB cable
  7. USB charger
    1. Any power source with 5 V and more than 720 mA will do
  8. Hookup wires


  1. Soldering iron
  2. Solder
  3. Wire cutters

Step 2: Circuit

This circuit is built with modules. Each circuit board contains two modules for a total of four modules in this project. If you want to expand or shrink this light, all you do is expand or decrease the number of modules in your circuit.

Each modules consists of:

  • 10 red LEDs and 4 blue LEDs.
  • The red LEDs are wired two in series along with a 56 ohm resistor.
  • The blue LEDs are wired with a 100 ohm resistor.
  • Five of these red pairs are wired in parallel with four of the blue LEDs.
  • A current draw of 180 mA

The complete circuit with four modules draws 720 mA.

Step 3: Soldering

Solder all the elements together according to the circuit diagram.

Then add some leads to all the common anodes (positive side) to each other, and connect all the common cathodes (negative side) to each other.

Rip open your USB cable and trim away the shielding and the data lines. The data lines are colored green and white. To avoid a short circuit, trim these cables at different lengths.

Then take your power leads from the USB cable and solder the red wire to any of the positive sides on the circuit board. Then solder the black wire to any of the negative sides on the circuit board.

After you have done this you can test your lights. Hopefully everything works!

If all the LEDs doesn't light up go back and check your wiring and soldering.

Step 4: Optional: 3D Printed Light Holder

If you have access to a 3D printer, I have included two STL files to print a holder for your lights.

One of the files, the one printed in the picture, have a slight angle on the legs to make it stand on top of my tiny green house.

You can download the files here.

If you don't have anything to set the holder on top off you can also hang the holder by the lights, as shown in the third picture.

You're finished!

If you wan't to see more of my projects check out my instructables or click here to read my web site.

Indoor Gardening Contest 2015

Third Prize in the
Indoor Gardening Contest 2015