Indoor Growing Setup - My New System

So my last post showed it would cost me $4.26 each month to grow two flats of seedlings under a fluorescent light fixture with two 40 watt bulbs. I can do better with LEDs. A few months ago I bought an LED light that is a foot square and has 225 little LEDs. It draws just 13.8 watts and can handle two flats (give or take, I do hear that is can handle anywhere from 2.25 sqft to 6 sqft - two flats are 2.8 sqft so we will see). For a month this is just 17.25% of the draw of two 40 watt bulbs or just $0.74/month.

They do have a major drawback though. Number one is that their start up costs are expensive. Mine ended up costing about $50. You can get a fluorescent light fixture for under $10 and bulbs for $3. So a set up can be just $15. Over time however you save yourself money. I'm guessing for me it will be $12/year in electricity costs (3 1/2 months). Also LEDs last years and years, probably close to 50 years if all you use them for is starting seedlings in the spring. Fluorescent lights don't last as long (and they fade) and ballasts also have to be replaced. But if I just look at electricity costs it will be about 3 years before it pays off. So in the long run it is cheaper and better for the planet.

The biggest issue with LEDs is that you have to know what you are going to grow. You need different LEDs for leaf growth than flower growth and if you are going for caratenoid levels in your plants you might choose even different LEDs. Unlike fluorescent lights which put out light in a wide spectrum, LEDs put out light in a very tiny spectrum, so you have to choose what exact color you want.

For those that have forgotten your high school science, the wavelength of light is measured in nanometers (nm). We see light from about 380nm (violet) to 750nm (red). Plants will absorb many wavelengths of light, but certain different wavelengths will make the plant grow differently. Chlorophyll absorbs the visible spectrum fairly well, except green (that is why it looks green to the eye). The different forms of chlorophyll absorb light best at different wavelengths, but they have big peaks in the blue and red.

Blue is very conductive to leafy growth. Blue light will stimulate nice green leaves and stocky growth. Caratenoids in the plants are formed best when the wavelength is between 450nm-470nm. Plant growth is probably best a little lower in wavelength. However if a plant gets nothing but blue light, the plant will not flower.

Red light promotes flowering of plants. Many sites claim that for growing you should have at least 90% red light because plants grow best with red. There is a caveat with that. The far red, at about 680nm, starts to be a problem. The plant will grow, but it will get leggy. Plants will grow best right before you hit that point so an LED close to that but below would be a good choice.

Of course you don't have to know all the wavelength issues if you are just buying a ready made grow light like I did. All you need to know is the difference between red and blue lights and pick the lights based on what plants you are growing. The people that make the grow lights have picked the wavelengths out for you already.

I'm growing seedlings for vegetables. I want stocky, leafy growth. I don't want anything to flower inside. I like promoting caratenoids since I'm eating the plants - though I'm unsure how long the benefits last. I went for an all blue. The LEDs are 460nm. I would prefer a 440nm light, but you take what the technology gives you. This one is pretty close to what I was after.

And the last problem with LEDs is that you only have one or two wavelengths of light so it looks funky to the naked eye. Everything near my blue light is hard to see. The colors are all off. If you used LEDs for an indoor plant in a living area it might be ugly and distracting. You would have to balance the light. A mixture of blue, red and green would probably be more appropriate for a setting where you have to see it all the time.

I still haven't gotten into where I'm putting this light, but again this post is getting a bit long and I'll get into that tomorrow. I promise no more science in the next installment.

Update from March: I have results how the LEDs did on my seedlings here. Go to the last paragraph on the page.