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DIY Plant Grow Light

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:

Parts

  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

Tools

  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.

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

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16 Discussions

Question 1 year ago on Step 1

can you give detailed information about led you use

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.

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 …

Diy indoor grow lights

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Note: We’ve recently updated this article to include the latest LED grow light technology in addition to common fluorescent shop lights which can also be used as grow lights. Since this article was originally written, the price of LED grow lights has decreased significantly, making them competitive with or in some cases even less expensive than fluorescent lighting.

Get a jumpstart on the warm and cool weather growing seasons AND grow food indoors year round with this DIY grow light setup.

Nevertheless, we’re able to grow food indoors AND in our yard 365 days per year. Yep, the afternoon after it hit five degrees, we uncovered our low tunnel beds and harvested spinach, kale, miner’s lettuce, chickweed, and cilantro for a salad.

Gardening: An Investment Worth Making

The National Gardening Association estimates that for every $1 you invest into your garden, you get $8 back.

It’s so gratifying to get daily garden harvests like this!

We love helping people learn how to maximize their Return On Investment (ROI) in their garden, get huge yields, and do it all using organic/permaculture growing methods. Of course, organic gardening has a range of benefits that extend far beyond money, as we’ve stated elsewhere.

The highest ROI comes from the stuff you can get or use for free. For instance, most people bag and throw out their fall leaves. However, leaves are an incredible source of free nutrition that you can use to feed your beneficial soil microbes, which ultimately produces more delicious organic food for you. With a couple hours of work, you can get hundreds or even thousands of dollars in return if you use those leaves for your garden.

Some of the other high-ROI things you can do in your garden do require an initial upfront investment of cash. For us, one of the things that has made the biggest difference—and created the highest ROI—is making an indoor DIY grow light system.

Our DIY indoor grow light system. The shelves are lonely in this picture, but for most of the year, they’re full of plants and seedlings.

Three Reasons to Make Your Own DIY Grow Light System

You don’t HAVE to have a grow light system in order to have great gardening success, but it certainly helps. Here are three reasons we recommend serious/more advanced home gardeners make a DIY grow light system:

1. Get a Jumpstart On Each Growing Season

In our Ag Zone, we start our spring and summer seeds indoors in late January through February, then transplant them outdoors after the last frost date.

This gives us (and our plants) a 2-3 month head start on the warm weather growing season. Translation: we get to start harvesting much earlier and for much longer than if we were to direct sow our seeds outdoors once the weather warmed up.

Trays of fall seedlings started indoors in late July/early August under our grow lights will be transplanted outdoors in September.

The same thing is true when we start our fall/winter seeds indoors in July-August, then transplant the seedlings outdoors in September-October. Also, if you’ve ever started seeds indoors without grow lights, you might also realize how hard it is to get enough sunlight through your windows (even south-facing windows) to keep your plants from getting weak and leggy.

2. Grow Food Indoors

There are indoor grow light systems you can use to grow large plants like tomatoes, but that’s not what we’re discussing here. The grow light system we use and recommend is designed for starting seeds for transplanting OR growing smaller plants like lettuces and other greens for indoor harvests.

Using the grow light system in this article, you can easily grow enough greens and/or microgreens to get a nice daily harvest. If you live in a particularly cold climate, this benefit might be especially attractive since it’s more difficult for you to grow outdoors during the winter.

An array of colorful microgreens growing under our indoor grow light system. Microgreens aren’t just beautiful and tasty, they also pack some serious nutrition. You can read our article about how (and why) to grow microgreens here.

3. Improve Seed Germination Rates

We start a lot of seeds indoors and outdoors. No matter where you live, an outdoor growing environment is always going to be a little less “stable” than an indoor growing environment— varying temperatures, soil moisture fluctuations, etc.

You’ll use less seeds and have a higher germination rate by starting your seeds indoors under grow lights. Not to mention, there might be hungry insects that are more than happy to chew down an emergent seedling soon after it punches through the soil surface in your garden—not so when you start your seeds indoors.

No matter how many times we see it happen, we still get a sense of joy seeing seeds germinate – especially if it’s still freezing cold and dreary outside!

You can improve your seed germination rates and plant survival rates by starting your main seedlings indoors, then transplanting them outdoors once they’re 6-9 weeks old. Plus, if you have an edible landscape, more mature plants are more immediately attractive.

How To Put Together Your Own Grow Light System

The grow light system we use has the following benefits/features:

  • Relatively inexpensive and can easily pay for itself in a single growing season.
  • Easy to break down and set up.
  • Made with parts that can be ordered from Amazon or found at large home improvement stores like Lowes or Home Depot.
  • Made with parts you never have to replace (except for the lightbulbs which need to be replaced every 10,000-50,000 light hours depending on manufacturer’s recommendations or visual signs that your plants are getting inadequate levels of light).
  • *Fluorescent bulbs produce 3x more light than incandescents, are energy efficient and non-heating. e.g. they’ll grow your plants without really impacting your energy or heating/cooling bills. (*Since this article was first written, the price of LED grow lights has come WAY down, so we also have LED grow light options listed below. LED grow lights are even more energy efficient than fluorescent bulbs.)
  • Made with adjustable parts so you can raise or lower each row or each light, AND remove or add shelves as needed.

1. The Parts for Your Indoor DIY Grow Light System

Below are the parts you’ll need to put together the exact grow light setup we use. Note: We’re providing info for two different sized grow light setups using the same materials (option 2 is just a miniature version):

  1. Option 1: LARGE Grow Light System – Five shelf system (74-in H x 48-in W x 18-in D). Technically, this system has 6 shelves, but you can’t hang lights above the top shelf, so there are only five shelves to put seed flats on. This LARGE Grow Light System is ideal if you’re growing plants for a large garden/edible landscape or if you plan to start/grow hundreds of plants indoors at the same time.
  2. Option 2: SMALL Grow Light System – Two shelf system (30-in H x 24-in W x 14-in D). Technically, this system has 3 shelves, but you can’t hang lights above the top shelf, so there are only two shelves to put seed flats on. The SMALL Grow Light System is ideal if you’re growing in a smaller garden/edible landscape or if you only plan to start/grow less than a hundred plants indoors at the same time.

Parts you’ll need to purchase and their cost via Amazon ( *please note that prices on Amazon change, sometimes daily, depending on sales and product availability ):

Materials List for LARGE Shelf Grow Light System:

  • 48″ Multi-Tier Steel Shelving Unit (48″L x 18″W x 82″H)/ there are a few product options here:
    • A tall 82″ chrome-colored unit with 6 adjustable tiers and wheels – product link | cost: (*since this is the lowest cost, we’ll use it in our total costs below)
    • Same tall 82″ unit as above (82″), but black-colored – product link | cost:
    • A shorter 72″ high steel unit with 6 adjustable tiers and wheels – product link | cost:
  • 10-Outlet Power Strip – product link | quantity needed: 1 | cost: (it’s a 2-pack)
  • Open Oval Chain (black finish) – product link | quantity needed: 1 ft strips x 20 total strips | cost: (whole roll, 50′) Depending on the lights you get, you may not need the chain since chains are sometimes included with the lights.
  • 20 S-hooks (various color finishes) – product link | quantity needed: 20 | cost: for a 30-pack
  • Zip Ties – product link | quantity needed: we used 10-12 but they come in a bag of 100 (you can never have too many zip ties around) | cost: $6.39
  • LIGHTING: Choose EITHER LED OR Fluorescent Lights. LEDs may be a touch more expensive up-front, but costs are quickly coming down on them and the benefit of having healthier plants may outweigh the expense.
    • LED Lights – These options assume 1 LED light strip per shelf. We’ve included a few options in case one is out of stock:
      • 48″ 64W Full Spectrum LED Light Strip – product link | quantity needed: 5 | cost: per unit
      • 48″ 60W Full Spectrum LED Light Strip – product link | quantity needed: 5 | cost: $45.99 per unit
      • 4 pack – 48″ 40W Full Spectrum LED Light Strips – product link | quantity needed: 1-2 | cost: per unit
    • Fluorescent Lights
      • 48″ Fluorescent Shop Light Housing – product link | quantity needed: 10 | cost: $15.50 per unit
      • 48″ COOL LIGHT Fluorescent Bulbs – two options depending on pricing and what’s in stock:
        • product link | quantity needed: we used 1 cool light bulb in each housing unit, or 10 total cool light bulbs | cost: /ten-pack
        • product link | quantity needed: same as above | cost: /ten-pack
      • 48″ WARM LIGHT Fluorescent Bulbs – product link | quantity: same as above | cost: /ten-pack
  • TOTAL COST: about $350 depending on current Amazon pricing

If you use fluorescent shop lights, S-hooks and chains allow you to hang your grow lights and adjust the distance between the bulbs and the plants as-needed (and as the plants grow taller).

Materials List for SMALL Grow Light System:

  • 3-Tier Steel Shelving Unit (13.11 x 23.15 x 29.90 inches) – product link | cost: (*Note that the reason this unit is so much less expensive than a 5 or 6-tier shelf is that the width and depth are much smaller, so you won’t be able to put as many plant trays on it)
  • 2-Outlet Power Strip – product link | quantity needed: 1 | cost: (it’s a 2-pack)
  • Zip Ties – product link | quantity needed: you’ll use 3-6 but they come in a bag of 100 (you can never have too many zip ties around) | cost: $6.39
  • 24″ LED grow light unit – product link | quantity needed: 2 | cost per unit: per unit
  • Note: You may be able to find fluorescent shop light housing + 24″ warm and cool light fluorescent bulbs at you local Lowes or Home Depot, but those items seem to be very rare now. Plus, that setup will actually cost about twice as much as the LED setup we recommend above.
  • (optional but recommended) Heavy duty shelf wheels | Note: these wheels allow you to easily move the entire grow light shelving system whenever, wherever you want – even when it’s full of seed trays. | product link (4-pack) | quantity: 1 | cost: $19.45
  • TOTAL COST: About $150 before taxes

2. Getting the Proper Bulbs

If you’re getting full spectrum LED grow lights, you can skip this section. If you’re getting/using fluorescent lights, you’ll want to carefully read this section…

As you probably know, light is essential for plant health/growth. Sunlight contains ROYGBIV, the full spectrum of colors of the rainbow that we all learned about in kindergarten.

The two most critically important light spectrums are RED and BLUE light.

  • Red spectrum light stimulates growth and flowering, but too much red light leads to tall, weak plants.
  • Blue spectrum light regulates the proper amount and distribution of plant growth, ensuring that all parts of the plant take on the proper size, shape and density.

The color of light created by each type of fluorescent bulb is determined by its interior phosphor coating. When using fluorescent bulbs, we recommend using a combination of these two types of fluorescent bulbs:

  • “Cool white” fluorescent bulbs offer Y/G/B (yellow, green, blue) spectrum lights for your plants. Cool bulbs have a kelvin range between 5000 – 6000K.
  • “Warm white” provides O/R (orange, red) spectrum light. Warm bulbs have a kelvin range between 2700 – 3500K.

So, install alternating cool and warm fluorescent bulbs into your light housing as indicated in the materials list above and shown in the image below. This way, you can mimic nearly the entire color spectrum of the sun, thus growing healthy seedlings and plants.

Alternating cool and warm fluorescent shop light bulbs. The bulbs don’t actually look red or blue to the naked eye.

3. Other Indoor Grow Light FAQs

Below are answers to the most frequently asked questions we get about our DIY indoor grow light setup:

1. How much indoor light hours do your plants need?

Answer: Each type of plant is a little different, but generally speaking, your edible garden plants will do fine with 10-14 hours of indoor light per day. You can buy a timer if you want or just set an alert on your phone/calendar to remind you to turn the lights on in the morning and off at night. Just like people, plants need darkness/rest, so try not to forget to turn your lights off.

More tips: 1) Plug one power strip into the other power strip so that you can just flip a single switch to turn all the lights on or off. 2) Use zip ties to attach your power strips to the side of your shelving unit AND to keep the power chords neat and organized.

2. How close do you let your plants go to the fluorescent grow lights?

Answer: Keep your plants about 2-3″ from your fluorescent lights. If your plants start looking thin, leggy and weak, move the lights closer to the tops of your plants using your adjustable chains and S-hooks. If the leaves get scalded, move your lights higher (very unlikely to happen unless your plants are directly touching the bulb).

Tomato seedlings being started indoors in February. Notice how close the lights are to the top of the plants – we keep the lights a few inches overhead. If the lights are touching the plants, your plants may get sunburn; if they’re too far away, your plants may become weak and leggy.

3. How often do I have to replace my fluorescent bulbs?

Answer: It depends on the bulbs you buy. Each manufacturer puts the estimated “lamp life” on the specs, which are often 20,000+ light hours. After a few years, if your bulbs are still working but your seedlings seem like they’re not growing as well, you may want to consider replacing them early.

4. What about growing under LED bulbs/lights?

Growing plants under LED bulbs is a little more complicated.

  • Sprouts & young seedlings – For sprouts and seedlings, you’ll want the tops of your plants to be 24-28″ overhead.
  • Growth stage – After your seedlings are a few weeks old, you can lower the LED lights to 18-24″ over the top of your plants.
  • Flowering/fruiting – If you’re growing plants all the way to production (ex. growing strawberries or tomatoes), you’ll want to lower your LED lights to a height of 12-18″ during this stage of development.

5. What trays, cells, etc. should I get and what starting mix should I get/make?

Answer: Since we’ve had comments and emails from this article asking what seed starting trays, etc we use, we’ll quickly provide a bit of info here, then refer you to more detailed articles/videos we’ve created on that topic:

  • Trays – Because we got tired of throwing away flimsy trays after one or two growing seasons, we now prefer these extra strength trays because they’re BPA-Free, SUPER durable, and also created by a local (to us) NC farmer who needed supplies that lasted longer than the current options: 5 pack & 10 pack
  • Heat mat – Essential for getting good seed germination when starting tomatoes, peppers, and other summer nightshades indoors: 48″ x 20″ heat mat & thermostat to control temps
  • More info – We have three free seed starting video classes (plus a free ebook) if you want to get the answers to all your seed starting questions. Plus, we also have a detailed guide showing you how to use Ladbrooke Soil Blocks.

Get a jumpstart on the warm and cool weather growing seasons AND easily grow food indoors year round with this DIY grow light setup.