Introducing the pieces of the puzzle…
The Circuit Diagram
My first attempt at building light to fake a plant into thinking its basking in the sun is based on this circuit diagram Richard had me draw at the end of our effort.
I decided to draw a (hopefully) more readable version.
Let’s meander through the components.
I cover what I learned about LED lighting for optimizing indoor plant growth in this post. For my first LED system, I chose to use LEDs that covered the spectrum of visible light that is most absorbed by plants during photosynthesis.
I chose CREE CXA2520 LEDs. From reading other blogposts by folks who set up similar systems, CREEs are known for their quality and have great specs as noted in the data sheet.
Here is a nice video on these LED modules.
And bought these cool LED holders that don’t require soldering when wiring the LED to the circuit.
To pick the size and number of LEDs that will do justice to the light requirements of plants, the ideal (and smart) method is to figure out the amount of LUX and wattage needed based on the size of the grow area, number of plants, and distance of the LED light source from the plant’s leaves and flowers. SuperAngryGuy’s posting on Reddit is a great read on this subject.
This would be the logical way of going about choosing how many LEDs to get. I did a bit of that but I don’t learn by designing thoroughly then doing. I have to incrementally learn by doing, figuring out why what I did was incorrect, adjust, and finally evolve into knowledge of what works for the scenario I have set up.
In the spirit of learning by doing – which I don’t even argue takes more time but is more effective for how I learn – I ordered two CREE CXA2520. One provides cool white light at a color temperature of 5000K, the CREE CXA2520-0000-000N00P40E7. One provides warm white light at a color temperature of 2700K, the CREE CXA2520-0000-000N00P20E8-ND.
I am concerned the cool temperature is not blue enough. SuperAngryGuy noted on Reddit: “Get the 6500K for veging, the 2700k for flowering.” I was anxious to get going so I went with 5000K. Time will tell and knowledge will blossom (sticking with a plant metaphor).
The Power Supply
I decided on this MeanWell power supply from LEDGroupBuy.com
Given my crude calculation, 250W / 48V seemed more than enough to power the LEDs. I also liked the way multiple LED drivers can be hooked up which means each driver does not need a separate power supply.
The LED Driver(s)
I ended up ordering two Meanwell LDD-1000H 1A 52Vout max. LED drivers
While this is a great driver, it’s maximum driver current is 1A. The LEDs I’m using (CREE CXA2520’s) have a maximum DC forward current of 1.25A. Drat. I should have ordered LDD’s that handled a little more than 1.25A. For now, I’ll use the LDD-1000H’s and not run the LEDs at full power. Hopefully this will prevent my LDDs from malfunction. I plan to use the dimmer switch to adjust the brightness of the LED and thus lower the amount of current the LED needs. This blunder is a testimony to reading data sheets more closely and matching up currents and voltages.
The brains behind this operation is an Arduino Uno.
I’m using the Uno because I have a few lying around. I will only be using one PWM pin for this circuit. Eventually I will hook up different sensors for water temperature, air temperature, pH, and TDS so that I can monitor the environmental variables that will affect the growth of a plant.
The Heat Sink
I couldn’t help myself. I tried out the circuit. Besides seeing huge white spots in most of my vision, the LED Array module started smoking. Of course you say – any numnut would know you must have a heat sink before testing. Well, like the person that learns stoves are hot by putting their hands on a lit burner, I seem to follow the same kind of exploratory learning.
TBD: Update after setting up with LED Arrays
Based on this blogpost: High-power LED grow light – a build log, I bought two Rosewill RCX-Z80-AL AMD CPU coolers – one for each LED Array. They were around $7 each.
I was going to get the heat sinks that “go” with the LED Holder
however, the cost was around $21. 3x the cost of the “not specifically for” heat sink I ended up ordering! I just couldn’t bring myself to pay 3x for something that didn’t seem to provide additional value other than being a perfect fit for the LED array holder – which does have a slight advantage in the ease-of-putting-together.
The LED Fixture
TBD: Update after setting up with LED Arrays
A few parts are still missing. These include:
- two aluminum angle pieces to mount the heat sinks holding the LED Arrays
- a piece of plastic above the LED arrays to protect them
- an aluminum reflector around the LED arrays to direct the light towards the plants
- chain or some other holder to mount the structure on top of the plants. Perhaps the best is to have these be adjustable so that as the plants grow, the L
Our next goal – put the circuit together and test it…the fun begins!