Do you enjoy gardening? - Yes
Do you enjoy electronics? - YES
Do you enjoy discovering how things operate? YES!
If you answered yes to all these questions than this is the guide for you!
Rather than writing another step-by-step guide to grow lights I will first explain how an LED works and then jump into constructing a real world application that brings everything together.
This instructable is meant to be a starting point for someone looking to get into electronics. If you already understand the science portion then please feel free to skip to step 6.
Let's get started!
Step 1: What Are LED's?
What is an LED? Tech term = Light Emitting Diodes
LEDs are part of a material category called Semiconductors.
- Semiconductors: can either conduct electricity under certain circumstances or not at all.
Semiconductors are made up of p-type and n-type silicon.
- P-type: a cluster of atoms that have vacant electron openings called "holes", postively charged (+)
- N-type: a cluster of atoms that have extra electrons, negatively charged (-)
LEDs are included in the category of electronic components called Diodes.
- Diodes: a semiconductor that has 2 terminals that correspond to p-type and n-type.
- p-type = anode terminal (+)
- n-type = cathode terminal (-)
Step 2: How Do LEDs Work?
Remember that LEDs are semiconductors so they have both p-type and n-type silicon.
- p-type: vacant electrons
- n-type: extra electrons
The PN interface of a diode dictates that current can only flow in one direction.
When an electric charge (battery) is connected to an LED, the current forces the extra n-type electrons to pass the junction to fill the vacant holes created by the p-type silicon.
For the n-type electrons to pass the junction the voltage needs to exceed a specific voltage rating.
- each LED has a different Voltage rating
LEDs are forward-bias and current-driven.
- Forward-Bias: the P side of a PN interface is made more positive (holes>extra electrons) = flowing current
- Reverse-Bias: the N side of a PN interface is made more negative (holes<extra electrons) = no current
Step 3: Laws That Control LEDs
Just like any other electronic component, LEDs have to abide by the basic laws of electricity in order to function.
3 fundamental electrical quantities:
- I = Current (measured in amperes)
- V = Voltage (measured in volts)
- R = Resistance (measured in Ohms) Ω
It's important to know these values when you choose the LED driver and power supply.
Without the proper power supply(voltage) the n-type electrons will not break the junction.
Without the proper LED driver there won't be enough continuous current to pass the electrons from the n side to the p side.
If you do not know one these values you can use Ohms law to find the other quantities.
- V = I * R
- I = V / R
- R = V / I
Another important quantity to consider in LEDs is Wattage.
Wattage is very important when considering LEDs for grow lights because of the distance between the bulb and plant.
- Watt: amount of energy used, a measure of brightness
- W = V * I (or) I^2 * R
Step 4: LED Driver and Power Supply
Quite frequently I've seen the terms LED driver and LED power supply used interchangeably but they are different.
LED driver has 2 functions:
- Current conversion, changes current from AC to DC.
- Current regulation, holds current at a constant ampere rate.
Remember that the PN interface of a diode will only allow current to flow in one direction.
- Alternating Current (AC): electrons can flow in both directions. example = wall outlet
- Direct Current (DC): electrons can flow backwards or forwards. example = batteries
Different LED drivers include:
- AC-DC driver: LEDs connect to wall outlet.
- DC-DC driver: LEDs connect to battery
LED power supply is considered a switching power supply and has 2 functions:
- Current conversion
- Voltage regulation, either increases, decreases, or keeps voltage constant.
Different LED power supplies include:
- Buck converter: (steps-down) output voltage < input voltage
- Boost Converter: (steps-up) output voltage > input voltage
- Buck-Boost Converter: can either step-up or step-down voltage
Main difference between the two:
- LED driver is a constant-current device.
- LED power supply is a constant-voltage device.
Step 5: Tools & Supplies
- Rotary tool
- Soldering iron
- 1 - Aluminum sheet
- 1 - Galvanized steel angle
- 1 - Galvanized steel hanger strap
- 1 - Metal epoxy
- 1 - Heatsink
- 2 - 9" Strap tie
Step 6: Light Fixture
Part 1: Frame
- The first thing you want to do is cut out the frame that will hold the LEDs and the heatsink. (Figure 1) has the measurements.
- After the frame is cut out bend back the flaps leaving about .5" on each side. I wanted to narrow the light range of the LEDs so it would only shine light on the plants below. (Figure 2)
- Attach the heatsink to the frame using metel epoxy. For the best application scar the surface of the frame and the heatsink before applying the epoxy. (Figure 3) It will take 24 hours for the bond to seal.
- Add the LEDs to the heatsink using the epoxy.
Part 2: Fixture
- Drill a hole on the back of the planter and using a 32 x 3/8" machine screw attach the 9" strap tie to the planter. (Figure 4)
- Connect the steel angle to the strap tie. (Figure 5)
Drill a hole at the ends of the frame, cut 2 pieces of the steel hanger strap at 3", and use the 40 x 1/2" machine screw to join the hanger strap to the frame.
Step 7: Choosing LEDs
Choosing the right LEDs for your project can be a little daunting especially with all the choices that are available. There a few things you should consider:
- Intensity - depending on how far away your fixture is from your plants.
- (12-24 inchs) = 3w or (>12 inchs) = 1w
- Color / Wavelength - different colors of the light spectrum have varying wavelengths that can effect different stages of plant growth.
- shorter wavelength = high energy (violet end of the spectrum)
- long wavelength = low energy (red end of the spectrum)
- Ultraviolet light (10nm - 400nm) - promotes the antioxidant activity of plants
- Blue light (430nm - 450nm) - stimulates root growth, ideal for seedlings during the vegetative stage
- Green light (495nm - 570nm) - least effective because the light is reflected back
- Red light (640nm - 680nm) - stimulates stem length, encourages flowering and fruit production
After choosing the LEDs the next step is to decide upon the LED driver.
Start by calculating the forward voltage rate of each LED, the seller usually lists the technical specs.
1w 660nm = 2.2v ~ 2.4v
1w Warm White = 3.4v ~ 3.6v
1w Cool White = 3.4v ~ 3.6v
1w 430nm = 3.4v ~ 3.6v
Total = Max 13.2v
Look for a 1W LED driver that can supply at least 13.2 volts and 350 milliamps.
Step 8: Wiring LEDs
The most important thing to remember is that an LED will not light up if the anode(+) is not connected to cathode(-). (+) ~ (-) ~ (+) ~ (-)
- Start by gluing the LEDs to the heatsink using the metal epoxy. (Figure 2)
- Cut 3 wires at a length of about 1/2" and 2 wires at 8".
- Solder the 1/2" wires from one LED to the next rotating between (+) ~ (-) ~ (+) ~ (-) ~ (+) ~ (-)
- Solder the 8" wires at each end.
Step 9: DC Power Source
The next step is to set up the project box that will hold the batteries, switch, and LED driver.
- Cut a hole out on the side of the project box for the switch.
- Drill a 1/4" hole on the long side of the project box, diagonal to the switch.
- Solder 1" wires onto the switch and attach it to the box.
- Connect the 9v battery holders together in series. (Figure 2)
- Cut four 1" wires and solder them to the (LED+, LED-, VIN+, VIN-) holes on the LED driver. (Figure 3)
Before I arranged everything in the project box I added a small platform to the LED driver by gluing leftover aluminum sheets to the bottom. The platform isn't necessary but it does make it easier to attach to the box.
- Solder one end of the switch to the VIN+ wire and the other end of the switch to the positive side of the battery pack. (Figure 4)
- Connect the negative side of the battery pack to the VIN- wire on the LED driver. (Figure 5)
- Feed the the two 8" wires from the LEDs through the hole on the side of the box.
- Attach the positive wire from the LED to the LED+ side on the LED driver.
- Attach the negative wire from the LED to the LED- side on the LED driver. (Figure 6)
Check the (Figure 1) diagram.
This method was not very effective with 1watt LEDs because I forgot to consider the amount of current that would drain from each battery. A 9v battery only supplies 500ma, so for an LED that requires 350ma the battery would only last for 1.8 hours before it is discharged.
A DC power source is more effective with 3mm and 5mm LEDs that have a max current of 20ma.
Step 10: AC Power Source
The second option for a power source is to directly connect an LED driver to an extension cord so you can plug it into any regular outlet.
For powering LEDs that require a large current rate to operate this will be your only option.
It's important to remember that voltage does play a big role in supplying the current needed for an LED but because voltage and current are directly proportional to one another, if voltage decreases then current will decrease.
I made the mistake of using a constant-voltage LED driver and for awhile it was working wonderfully. But after a power surge hit my LEDs blew out. The spike in electricity caused the voltage to increase exponentially and in turn significantly increase the current.
Step 11: Conclusion
After my first couple attempts at building small LED fixtures there were a few things I picked up on that I felt weren't covered enough in other topics and discussions online. I wrote this instructable to address the topics that aren't discussed but are crucial to understand if you want to design an LED fixture of your own.
For me when I'm building something I need to understand the mechanics behind the product before I can construct anything. Instead of writing an instructional guide that layouts the framework for making an LED fixture I chose to focus on the science that drives LEDs. A Why rather than a How.
I am not an engineer nor am I an electrician but I am an avid electronic hobbyist. My hope is that after reading this instructional guide you'll have a greater understanding of LED grow lights and learn from the mistakes I've made.
If there was something that wasn't included in this guide or that you felt should have been discussed in greater detail please feel free to leave a comment.
The best way to learn about electronics is by getting your hands dirty and making real-world applications that test the scientific theories.