Sunday, January 4, 2009

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.


  1. Daphne,
    Wow!! Thanks so much for your informative post!! I am thinking that since I want to start seeds for annuals and veggies, perhaps I would be better off getting a ready made grow light. There are some bulbs from a company called SunLite that have super-efficient T-8 fluorescent bulbs — with full-spectrum light. I was curious as to the energy cost of running this little seed-starting operation, and your posts have helped to give me at least a ballpark figure, which really helps. I'll be tuning in tomorrow... : )

  2. Ow! My brain hurts now....ha! That was very informative stuff about the light criteria for plant growth. Those LED's sure will last along time, I bet. Thanks for sharing the information.


  3. Daphne, that's some really great information - thanks! Where did you find the lights?

  4. Looks like a great setup and save some money and possibly get healthier seedlings at the same time. As for your visibility issue (our eyes not working so well with just blue light) there is always white LED lights as you can see from my plant color spectrum post that the intensities and wavelength for blue light are pretty close though not sure if there is enough red light to cause leggy seedlings... Guess it is time for me to do yet another experiment. Simpler solution may be setup a little desk lamp for inspection purposes. I am definitely looking forward to seeing the final setup.

  5. Liisa: Your welcome. I know I'm taking my time answering your earlier comment, but I'm getting there.

    EngineeredGarden: Ah it is good to exercise the brain, though I'm guessing you do it all the time when you are building things for the garden. Your setup is so much more elaborate than mine.

    Michelle: I bought mine on ebay from LEDwholesalers_Inc. I don't greatly recommend them. The first panel they sent me didn't work. I opened it up and didn't see anything that could have fallen off during shipment. The wiring seemed secure, so I'm guessing their QA could use some help. I sent it back and got a new one that did work, but they didn't refund my mailing fees, so it cost me more than what I bid for it. That always bugs me. There are others that sell there too that might be better.

    The Cheap Vegetable Gardener: The blue light will be blocked from the rest of the laundry room (where my setup is), so it shouldn't impact me much except when I look at my plants. To see them, I'll probably just take them off the shelf away from the blue light to look at them occasionally. If it ends up driving my crazy, I'll look into mixed LEDs.

  6. Daphne, you are amazing. I had no idea about the different wavelengths and the color spectrum and all that. I think it's wonderful that you're not just considering your pocketbook, but the environment, too.


  7. No more science? Awwww...come on...this post is 48% of the reason why I keep coming back to read here. ;)

    I actually tried to get my husband to come over and read with me it was so interesting.

  8. Ara: Thanks.

    Tam: LOL You can always look up more science. Go look up chlorophyll in Wikipedia. They have a really nice in vitro chlorophyll absorption chart (toward the bottom). Most of the info though is pretty useless to actually growing plants.

  9. I enjoyed reading your blog ~ thanks for posting such useful content
    Growing Plants