DIY Plant Grow Light





Introduction: DIY Plant Grow Light

Third Prize in the
Indoor Gardening Contest 2015

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.



  • Homemade Gifts Contest 2017

    Homemade Gifts Contest 2017
  • Remote Control Contest 2017

    Remote Control Contest 2017
  • Design For Kids Challenge

    Design For Kids Challenge

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Questions & Answers


A couple of things grow lamps don't use just red and Blue LEDs The NASA lamps use very specific wavelengths of red 660nm, 640nm and blue is 440nm and 465nm (I am going from memory on the wavelengths so one or two might be a little off) Most common red LEDs are 625nm which may not work well for plants.

Also some plants use yellow and orange light to guide gowth. While many plants do well with just red and blue, some don't. My orchids did not do very well with just red and blue. But when using white LED of about the same overall power level they had better growth

"the reason why you don't think this is enough light is because unlike nasa you are using regular LEDs. you need to use at least 1W high power LEDs."

The power level of the LED doesn't matter to plants. Plants do care about how bright the light is. You can use low power led successfully but you need more of them. Using 1W or larger LEDs means you can use fewer LEDs to get the same amount of light but then you have to deal with heat issues.

' the problem is not the spectrum. it is how far the lights can travel. with what you have made it only reaches to the very near leaves and not the rest. "

A photon of light will travel a light year with no loss in power. The issue hear is not power or spectrum. Instead it is a mater of focus and the size of the light. The light from LEDs spreads out as it travels and as it spreads out the brightness of the light drops. Many high end LEDS use lenses and reflectors to control the spread of light. The other aspect of this you want light to get past the outer leaves to reach leaves closer to the stem of the plant. You do this by increasing the area of the light source. A small 3by 3" LED array will only light up the outer layer of leaves.

However if you reconfigured the LEDs into a 1" by 9" light bar some of the light will travel straight down to the top leaves while some light will travel at a steep angle, miss the top leaves, and then hit the lower leaves. Larger light sources have less distinct shadows and better light penetration.

Currently my orchids are growing under a white lamp I made from LED strip lights. Each led is about 1/4 watt and the entire array consumed about 35 watts. It has about 300 LEDs. The entire array is 6" by 24". There are no distinct shadows from this lamp and I get very good light penetration. After I built this lamp all my orchids started to show normal growth. Since September one has already flowered, two others are in flower and 1 has started a new flower stem. I have 3 other orchids one finished flowering several months ago and the other 2 are new and likely need to grow more before they will flower.

Mate you just dropped some serious knowledge!

I really like the idea of having the LEDs more spread out. For this, the LED strips you use would be perfect.

What do you use as a power source and do you have any heating issues with your setup?

I used a 12V led light strips. the lamp is powered by a 60W 12VDC power supply. The entire glass panel is warm to the touch but not hot (about 100F). I do not have a constant current power source, fan or heat sink. At the temperature it is operating at, a constant current source is not required.

Nice set up.

For me, the biggest hurdle of a bigger grow light would be to get a power source as cheap as possible.

Use 12v 2 amperes that would be perfect. Also attach heat sink with the board and attach the fan for overcome the heating issue.

check mine instructable

There's actually no heat problem at all. The nice thing about this running on 5V is that it can be powered by a spare phone charger and I don't need to add a noisy fan or a bulky heat sink!

You're right my friend.

I'll look into uppgrading the light with brighter LEDs later on.

That's a nice collection you got there!

i really like your setup. especially the printed arm. the lights you have made can be used to wake up seedlings but not for much longer. the problem is not the spectrum. it is how far the lights can travel. with what you have made it only reaches to the very near leaves and not the rest. and the light has to be really close to the plant


more wattage means they travel longer. each 1W led uses upto 350mA. 3W leds use 700mA, same space same size can reach upto 100W, thats around 900w equivalent from a space the size of your fingertip. at these stages we need serious cooling solutions.
but depending on what you need, especially for small indoor gardens - like an herb garden, you can get away with using just 1-4W. i grow seedlings under 1W and here also you can see a +2yr old citrus grown using only 4W since seed.

I see. I've looked into some more high powered LEDs like you've described.

My only concern is finding a suitable power supply because those LEDs draw a lot of current.

I'm guessing an old laptop charger would be perfect for those lights!