Introduction: Classroom Grow Lights
Teaching our next generation about the technologies of the future is becoming increasingly important. In Australia food produce is one of our biggest industries and continues to grow with our population. Today traditional techniques for growing plants and animals are beginning to falter and we need to look forward to technology to ensure a stable food source for the future.
In this experiment I want to look at the effectiveness of grow lights compared to sunlight. The effects of this type of growing on plants and teach in turn about how we can effectively grow indoors and explore both the positives and the downsides to doing so. With this information we will discover why a trend of indoor farms are beginning to form around the world.
- Grade 5-12
- Horticulture (Chemistry)
- Electronics (Physics)
- Full spectrum LED Strip
- 5V Power supply (choose Appropriate amperage explained below US EU Plug link only)
- Tray to plant into (found mine at nursery)
- Plants of your choice
Step 1: Lesson Plan/How to Teach
How to teach this will come down to the time you have allocated. The overall results will take a few weeks however bulk of the concept and discussion could take place in one lesson.
- Discussion of current farming techniques eg. farmer tracker fields etc Discuss issues in current farms eg require large areas, pests, water, soil nutrients, distance from city's.
- Video to give students an idea of process
- Discuss benefits of vertical farms
- Break the students into as many groups as required and have each group create a different setup (Plant in natural sunlight, 10 LED's, 5 LED's, No light, low light, light time)
- Have the students predict the outcome of there project and why using previously discussed ideas,
- Continue to care for plant for a few weeks
- Once plants are significantly grown have students look and results and compare them to their prediction
This lesson plan is loosely planed to allow for alterations to suit the class and your learning intentions, an alternative is to just have one setup for the entire class.
Step 2: The Science
This project is an exciting way to explore so many different properties of horticulture and photosynthesis of plants. In this section I will aim to list off the ones that I believe to be most important for students however there is so many more ideas that can be explored past what will be listed here.
Light wavelength - effect on photosynthesis
Perhaps the most important concept to understand during this project is that plants use many different wavelengths of light, these are all usually supplied from the sun. In a sunlight free environment we need to be able to recreate these waves so that photosynthesis can occur.
Different wavelengths and plant effects
- Red lighting: 650-660nm, 620-630nm, the best wavelength for plants blossom.
- Blue lighting: 430-440nm, 450-460nm, the best wavelength for promoting the growth of plant nutrition and plants growth.
- White lighting: full spectrum, wide color temperature, complement other wavelengths, to increase brightness.
- UV-lighting: 380-400nm, increasing the chlorophyll, increasing crop yield, promoting seed germination, also disinfection antiseptic effect.
- Infrared light: 730nm, the best wavelength to influence phytochrome plants, can promote flowering and prolong flowering.
What this means for us?
Okay so we need different color LED's? well yes but careful attention to the wavelength here more than the colour is important! Using standard red LED's from Ebay might result in so very dead plants. what we require is full spectrum LED's and all this really means is that the light produced by these LED's is within what our plants need.
Red to Blue Ratio:
Secondly we need both red and blue most importantly to allow for the plant to grow and blossom strong. This ratio depends strongly on what you plan to grow. I will add a link below to the full discussion on this but here is the overview.
- The light RED: BLUE rated at 3:1, 4:1, 5:1 are good to accelerate the growth of leaf, for plant-like Cabbage, Lettuce, Spinach and so on.
- The light RED: BLUE rated at 5:1, 6:1 is good for the plant that needs light fill in the whole growth period, like the Leaf Succulent.
- The light RED: BLUE rated at 7:1, 8:1, 9:1 are good to accelerate the growth of root, for plant-like Eggplant, Tomato, Long Bean, Color Pepper, Cucumber and so on.
Day night cycle
So like humans plants need rest so it is important to have the lights only on for around 16-18 hours per day to allow for the plants to grow.
How far away to place the LED lights
This is a little harder to work out for our LED's as there are not many articles on their optimal usage. As these are lowered powered than most HID lights (HID is commonly used rather than LED's) I believe a height of 20cm (8inches) should work just fine as our LED's will let off little heat.
Step 3: The Experiment!!
For this section I'm going to make a lot of different suggestions, show what I did and from this you can decide what you would like to do in your classroom.
These lights come in 5m lengths powering the whole string uses around 4.55 Amps so for each meter we should assume around 1 amp draw. The tray I used was only small (can be found at any nursery) requiring around 2m of LED's so I decided to use a 2 Amp power supply remember that more amps is better than not enough.
I cut my strips to lengths and spaced them around 40mm apart used a Stanley knife to remove the silicon (if you got waterproof version) soldering wires of the appropriate lengths to the + and - pads. and insert the cables into dc barrel jack to there corresponding + and -.
PLEASE NOTE- I'm unsure if current direction matters on these LED's however keep note of how they came off the strip eg keep them end to end as they came off the wheel (view picture with ruler you can see that the LED resistor pattern is different and thus connected as they were on strip)
Wiring all done test them out!
I next positioned them above my tray stuck them down using the tape on back and some extra tape. Planted out my tray, gave them a light water and waited for the plants to emerge. (don't forget to turn off the lights for a few hours as discussed above to allow rest)
Okay so some of that would seem a little daunting for those of you that don't work with electronics to often... fear not! If you are uncomfortable with all the soldering and setup you can use the optional connectors listed above to join the LED's and wires easily and solder free! also instead of cutting the LEDs apart like I did you could keep them together using smaller less wide pots and using a 5 amp power supply instead.
for variables you could black out different numbers on LED's using tape and find the optimal colors and number of colors. The LED's ares sold in different patterns I used a 3/1 (Red/Blue) but this is another variable you can easily test without much setup.
Step 4: Results
So much to my surprise I had some seriously awesome results, there is something super satisfying about growing a plant inside in a dark room. These things popped out of the ground and took off like there was no tomorrow! seriously you can almost see them moving.
currently it's winter here and we are around 16 degrees Celsius max and a low of 4 most days. Growing plants like this outside at this time of year would either be very difficult or at least very slow.
From the first image to the last is about one week. They are very strong plants and perfectly untouched by pests or disease. Until now I could't really comprehend how this kind of growing could ever be viable but with so much control over the plants, their environment, pests and their incredible growth rate under these ideal conditions I can understand the massive savings and profits that this kind of system at scale could present.
Step 5: Thankyou
Thanks for reading my Instructable be sure to check out all my other awesome Instructables here and follow me to keep up to date with all my future projects!
Hopefully this fun project works well in your school and as always if you have any questions leave a comment and I'll be sure to reply ASAP!
Participated in the
Classroom Science Contest