LED grow lights are a fairly new method of growing plants. They are very efficient because they produce only the wavelengths needed for photosynthesis and very little heat. Most grow lights produce a lot of green light is reflected by the leaves.This grow light costs up to $40 to make and doesn't cost much to run. It won't burn your plants even if you put them very close.
In this Instructable you will learn:
How the color of light sources affects the growth rate of plants
How a grow light system can be made from high power LEDs, PC heatsink, and other electronic components
Why it is important to properly drive high powered LEDs
Why a light meter is essential when designing a grow light system
How LED performance can be optimized
How an LED grow light system can be designed so that plants receive more light
Step 1: Things Needed
2 x 3W royal blue LED (445nm)
6 x 3W deep red LED (660 nm)
Heatsink with fan
Solder (lead free when growing edibles)
Note: You can get LEDs at e-Bay for as little as $2 each when you purchase them whole sale.
1A fuse with clips
Resistors (0.33, 0.56, 1, and 100k ohm)
N-channel MOSFET (eg. IRF540N) with heatsink
General purpose NPN transistor (eg. 2N3904)
1A adapters (see below)
DC adapter socket
26 gauge wires (Correct sizing for current ratings can be found here)
Finding the right voltage adapter
You can find adapters at a low price at used computer stores, second hand stores, electronic stores, and ebay. To supply enough voltage, you add up the LEDs' forward voltage with the required overhead voltage (0.6V here).
Supply voltage for red LEDs=6*2.5V+0.6V=15.6V
Supply voltage for blue LEDs=2*3.8V+0.6V=8.2V
Note: Fuses and wires may cause a small drop of voltage so you may want an overhead voltage of at least 1V. The voltage difference is larger with thinner or longer wires. It can be significant if the current is high..
Multimeter capable of measuring several amps
Light meter (optional)
Electric timer (optional)
Step 2: Grow Light
High power LEDs require a constant current source so that they last a long time. This means they cannot be connected directly to a power source. There are many options for LED drivers. I used the MOSFET regulator below. Before soldering, you should test the circuit on a breadboard. The second diagram included the brightness settings. I used an on-off-on two pole switch.
Mount to a Heatsink
These LEDs also require a heatsink or they will get extremely hot. They were mounted epoxy. If the screws are too loose, you can glue them into the holes. The heatsink I used can hold a maximum of 8 LEDs. You can strain relief the wires with hot glue. With the heatsink fan, the heatsink doesn't get hot.
Tie the Wires Together
Step 3: Housing for Plants
Step 4: Cost and Power Consumption
Red LEDs: 14.55V x 0.68A = 9.89W
Red LEDs with driver:16.13V x 0.68A 10.97W
Blue LEDs: 6.98V x 0.64A = 4.47W
Blue LEDs with driver: 10.24V x 0.64A = 6.55W
Watts used by grow light: 17.5 W*
Cost to run the grow light: 17.5W x (1kW/1000kW) x $0.10 per kWh x 16 hours x 365 days per year = $10.22 per year
Watts Used by System (Low Setting)
Red LEDs: 13.13V x 0.32A = 4.20W
Red LEDs with driver = 16.19V x 0.32A = 5.18W
Blue LEDs: 6.28V x 0.31A = 1.95W
Blue LEDs with driver:10.64V x 0.31A = 3.30W
Watts used by grow light: 8.48 W*
Cost to run the grow light: 8.48W x (1kW/1000kW) x $0.10 per kWh x 16 hours x 365 days per year = $4.95 per year
*Power supplies are excluded.
For conventional 250W grow lights, the cost is about $146 with similar schedules.
Measuring Power Consumption
The power consumption can be calculated by measuring the voltage across the circuit and measuring the current across the switch while the LEDs are off and solving the equation:
If you want to know the LED's voltage drop, measure the voltage across the LED's. The current across the LED(s) is similar to the current across the entire circuit because the resistance of R1 is very high. Note that the power dissipated by LEDs is not always equal to the labelled voltage.
Cost of the Grow Light
MOSFET with heatsink: $7
NPN transistors (per package): $1
Resistors (4 packs): $2
16V laptop charger: Free
12V adapter: $3
9V adapter: $3
Fuse clips: $1
Step 5: How Much Light Does This Put Out?
A light meter can be used. They measure wavelengths which are useful for plant growth.
Ways to Increase Light Output
Use SMD LEDs which take up less space on heatsink
Step 6: Other Tips
With an electric timer, you can actually "change the seasons" by adjusting the length of the dark period. For cool season vegetables, 12 hours of sunlight is recommended. Warm season plants like roots and most fruits and flowers require longer days like 16 hours of sunlight. Feel free to experiment.
Use a Heating Mat
Since grow LEDs produce very little heat, heating mats are useful in cool conditions.
Use Far Red (730 nm) LEDs
If you can find far red LEDs, you can try using them to control flowering. When exposed to far red at the end of the day, plants would think they have been exposed to red light for a shorter period than actual.