Monday, March 28, 2011

More on Grow Lights

You may recall that a while back I posted an article on growing plants indoors under lights. The article recommended eschewing the purchase of expensive grow light systems and instead growing under simple two-bulb workshop ballasts, each with one soft and one cool white fluorescent bulb. These two inexpensive, readily available bulb types have just the right kind of light to stimulate plant growth.

After posting Read This Before You Buy Grow Lights, I received a couple of responses to the post, mostly from commercial vendors of grow lights of various types. I found one of those messages intriguing because it presented a concept entirely foreign to me: growing under LEDs (Light-emitting Diodes). Here's the letter sent by Alex McQuown, Research Director of EcogroLED in Riverside, CA:

"Hi Heather, I read your grow light article and I thought I'd give you a few bits of clarification.

"Fluorescent lamps are actually a pretty poor choice for indoor gardening. The output maintenance for the bulbs is rather dismal (as is the lifespan of any electrode-based lamp,) the heavy amounts of green light actually interfere with some aspects of plant cellular division and maturation, and the phosphors are not hitting optimal chlorophyll absorption peaks (two in red and two in blue, plus another huge photomorphogenic peak in the UVB range and potentially a peak in the IR range.) Also, due to the low efficiency of fluorescent lamps (approximately 17%) a ton of energy is wasted.

"You'll be forced to change those bulbs out almost every year to maintain the brightest output possible. Canopy penetration is pretty dismal as well, with a typical T8 lamp only being as intense as the sun almost literally on top of the bulb - this means the usable photon flux density is within a very short range - about 8 inches from the light is the maximum usable distance before the umol level drops below usable densities.

"For just over a hundred bucks you could buy a 50w LED system that would've covered that entire setup, plus increased your productivity several times over, you'd (practically) never have to worry about replacement, and the coverage is out of this world….

"You should consider LED lighting."

* * * * *

Unsure of how to respond, I forwarded McQuown's message to my UW-Extension Master Gardener Training instructor, Sharon Morrisey, who serves as a Consumer Horticulture Agent for the Extension. She was the one who taught us Master Gardeners-in-training that expensive grow lights aren't necessary for growing indoors. Morrisey, too, was unfamiliar with using LEDs as grow lights, so she communicated with her fellow "co-horts" at the Extension. UW-EX greenhouse manager Johanna Oosterwyk responded: she doesn't recommend LED grow lights for hobbyists, though she agreed with McQuown that LEDs are more efficient at the commercial level. Here's Oosterwyk's response:

"[McQuown] is right on several counts. An LED fixture is more efficient and can produce a better growth response than a traditional fluorescent, incandescent or HID fixture. There are two reasons for this. First, the energy efficiency of LEDs is well established -- you get considerably more light energy per watt of electrical energy. Second, although individual LEDs are small and their output is moderate, they emit light in a very narrow wavelength. Manufacturers use this as an advantage by wiring together an array of LEDs that emit in the wavelengths that plants absorb best (red and blue). As you guys remember from class, both blue and red are needed for specific development responses (germination and flowering respectively). So not only is efficiency increased in production it's increased in absorption and use as well.

"However, I would still not recommend them to hobby growers. The initial costs are too high (though coming down) and for houseplants you just don't need that kind of radiation output. In addition, though you won't find yourself replacing bulbs every few years, when you do have to replace LEDs you will have to replace the entire fixture (or at least the entire light array), not just a single LED. They are all wired together on an electrical board so it is not a simple matter to swap one out. LEDs are supposed to be long-lived, but their lifespan can be greatly reduced by over-heating, so an effective cooling mechanism is essential or you will be replacing your fixture long before the 50000 hours he cites.

"Also, I don't know anything about the quality of [EcogroLED]; for a comparable product look here:

"LED growth fixtures are new enough that manufacturers are still working out the bugs. Which LEDs are best? In what combinations? Does the housing keep them cool enough? It will be interesting to watch them develop and in the next 5-10 years. Maybe we will be recommending them to hobbyists. There's a large study being undertaken by several universities and Orbital Technologies of Madison (former students of UW Hort Prof Ted Tibbits) more info here."

* * * * *

Did you get all that? I know. It's pretty complicated stuff. The bottom line, I think, is that the two-fluorescent bulb approach works fine for those wishing to give a few flats of veggie seeds a head start indoors in early spring. For anecdotal proof of this, check out the progress of my two flats of lettuce started in mid-winter. This is how my "Pablo Lettuce" seedlings looked on January 28:

And here they are now (see flat on far left):

I've already harvested some of this lettuce and it tastes great!

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