40W LED Grow Light




Introduction: 40W LED Grow Light

About: i sell peppers and seedlings on my website http://juanitospeppers.com

I wanted a led light that was cheap and would perform the same as or better than t8 / t5 fluorescent lights.

In this instructable i make a 50w led bar to replace a 4' 2 tube fixture

The cost is around 23$.

Step 1: Tools & Materials


soldering iron


(optional multimeter for testing)

(optional 2 aa batteries for testing)

Materials 23$

18 - 21 pieces - 3w LED with star heatsink (ebay)

led driver 600mA 36-60v (ebay Constant Current Driver for 12-18pcs 3W High Power)

2 prong power cord (ebay)

thermal adhesive (ebay)

~4.50$ 42in of aluminum U channel(i bought 8' and cut in half) (lowes, home depot)

.50$ solder

1$ 8' of 20-16 gauge wire

1$ electrical tape

LED Selection:

I picked a 2 red : 1 cool white ratio.
Red has been shown to be most important and its possible to grow plants with only red light(although there are some problems). To reduce strain on the plant we give it most of the other wavelengths in small amount (from the white) and we pick cool white to give it more blue. We need about 12% blue light. With cool white being almost 50% blue light we get around 15%. I go 1 red (620nm) 1 far red(660nm) to get the most optimal light for the different photosynthesis peaks. White is easier on the eyes and provides all the other wavelengths in smaller amounts so i think its better than going just only red and blue.

Although going red and blue is possible. If you want to do that go like 5 red : 1 royal blue.

Also if you don't want to deal with wavelengths you can just go 100% white that's fine.

leds need to all be the same mA, voltage can be different.

Step 2: Schematic

Step 3: Aluminium

Cut to length (42")

remove any stickers

Step 4: Driver

attach driver to open part of u channel with some elec tape

strip / attach /solder joints between driver and power cord

cover with tape

wrap end of alum with tape to make a table on open u end.

secure cord to aluminum by making a sandwich around the cord

Step 5: LEDS

plan out the positioning..

since i have 21 leds in 42inches i did about 1.75 in spacing

put dot of thermal adhesive on bottom of led star

press firmly to aluminium

wait for adhesive to cure

i waited overnight just to be sure.

Step 6: Wire

cut wire to length and strip the ends (this takes a long time lol)

tin the terminals on the led star u will be using also tin the end of the wires

solder the wire ends to the terminals

attach to driver

measure wire from far end of string back to the driver

strip / wrap / solder

you can secure the line with tape every foot to the side of the aluminum so it's not in the way.

run line directly from driver to close end.

Step 7: Done

plug it in see if it works, if it does, yay

Step 8: =[ It Doesnt Work

doesn't light..

Get your 2 AA's tape together

put a wire on each end and put to the respective led terminals

(its ok if your hand touches this it won't shock you because so low voltages / amps)

if you find a bad led, just remove it and put a new one on there.

flashing light..

you don't have enough leds in there, you're below the minimum for the driver. (add more leds)

one of your leds is grounded to the aluminium causing a short (do the test with batteries above on each led to find the bad one)

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    8 Discussions


    5 years ago on Introduction

    I'm new to DIY and I'm trying to build something similar to this for growing lettuce and getting my chillis started. I've looked at a lot of instructables, but this one and the one by tvgoss are the ones that stand out.

    I was wondering, is there any reason in particular for choosing LED's with a star heatsink over LED strip lights if I go white LEDs only? Also, how large is the area you are growing in under these lights? My grow area will probably be around 23"x20"x19".


    Reply 5 years ago on Introduction

    the led strips are certainly easier to source and solder together, but they use smaller leds so require many more. Smaller leds have lesser canopy penetration and need to be placed closer to plants. Also more parts = more chances for failure.
    For me if a led fails it's very easy to just fire up the solder iron remove the old one and stick a new one on. With the stip you are either going to cut out a section and solder it back on or scrap that whole section and put a new one.
    Controlling spectrum is another benefit. I can run as many different leds as i want where it seems strip lights are only a few colors or rgb.
    If you are going all white, then the canopy penetration / light intensity is the only thing you would worry about i guess.

    i'm using 2 light bars for 4x2x2' aka 1 bar per 4x1x2'
    if you made this led bar, but cut the alum it so its like a square that'd be good for your 2x2x2 space


    Reply 5 years ago on Introduction

    Thanks. I didn't realise canopy penetration would be such a problem. I'll try to find out if people using strip lights consider it a major issue. To gain control over spectrum I was considering a combination of cool and warm white strips.

    I guess the larger lights you use create a lot more heat than a 5630 LED strip would?

    Could you tell me, approximately, how much power your lights use?


    Reply 5 years ago on Introduction

    spectrum is up to you bud, there is tons of literature / debate on what's best, red blue white uv infared etc

    yeah more heat

    50-60w per driver(21pcs led)


    5 years ago on Introduction

    I've done an almost identical thing for a work light using 18 3 Watt Warm White LED's on a 4 foot piece of channel. I was wondering how you handle the heat produced? I used 3/4 inch channel and it gets hot enough that I want a fan on it.

    Also as a tip you can use the aluminum channel as your negative lead, just attach the Driver to the channel directly and attach the negative contact of the last LED in the series to the channel... eliminates the long floppy wire.


    Reply 5 years ago on Introduction

    mine runs within manufacturer temp spec. The whites are much hotter than the reds.


    5 years ago

    Have you grown/started plants with this set-up yet? I'm mostly interested in starting plants and I thought plants preferred more blue early in life and more red later in the fruiting/flowering stages.


    Reply 5 years ago on Introduction

    yeah i use this setup for starting pepper plants, going to try some kratky lettuce later this year.