LED growing lights
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Are LED growing lights better than fluorescent, metal halide, or high pressure sodium grow lights? Will they improve plant growth, and will they use less electricity? Is growing plants with LED growing lights environmentally friendly?
Plants don't use the full visible spectrum to photosynthecize. They predominantly use cool (violet-blue and blue), and warm (orange-red) wavelengths, which is a reflection of the typical colors of natural night on a seasonal basis. In the summer months when the sun is more directly overhead, cool colors predominate and tend to encourage healthy vegetative growth, while in spring and fall warm colors take over and tend to encourage flowering and fruiting.
A typical metal halide grow light puts out much of its output in wavelength ranges that plants do not use - cyan, green, yellow - and very little in the violet or blue regions. So with a metal halide grow light you are typically wasting much of the light shining down on your plants. A 'daylight' metal halide light is more in the blue spectrum and so is useful for the vegetative stage of growth but not for flowering or fruiting. High pressure sodium lights tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting.
You can create your own LED growing lights by combining red and blue LED lights in roughly a two- to-one proportion (two blue to one red), or buy an LED set designed specifically for indoor growing, which has blue and red LED grow lights in an appropriate proportion. LED grow lights have the benefit of low heat output, so you don't need to worry about drying out the soil or scorching the plants, and they use very little electricity. For example, GlowPanel LED growing lights cover a 1.5 square foot area (they are roughly 15 inches on a side) and consume just 14 watts. For growing purposes, this light would be suitable for starting seedlings or for growing herbs or lettuce indoors, but is at the lower end of required light output for growing vegetables.
Is it 'green' to use LED growing lights? Well, it's definitely an improvement to switch from any of the other technologies, as the amount of electricity you'll use for the same amount of growth is reduced significantly, because of the concentration of light in the desired ranges of the spectrum, and because of the improved efficiency of LEDs. But in absolute terms, I personally feel that LED growing lights should be used sparingly, unless you have a source of carbon-neutral electricity that no one else has a use for.
Why? Let's consider a 6-square-foot herb garden using the GlowPanel LED growing lights. These lights consume 14 watts each for 1.5 square feet, or 56 watts for the 6-square foot garden. The lights should be on about 12-16 hours a day for growing herbs or lettuce. Let's assume 12 hours to be conservative. That meas we're using 12 x 56 watts per day, or 672 watt-hours. Over a three month period, that becomes about 60 kilowatt hours.
Let's assume that 6-square foot garden produces 12 healthy heads of lettuce over the three month period. Each head of lettuce has therefore cost you 5 kilowatt hours of electricity, and might weigh a pound wet weight - and at about 95% water content, would consist of less than an ounce of dried organic matter.
If you've read my Energy saving facts article you'll remember that a kilowatt hour of electricity, if produced from coal, requires about 1 lb of coal to be burned, and produces just under 3 lb of CO2 (the main greenhouse gas behind climate change). Remember that coal is nothing more than fossilized plants. So in essence, you are consuming 5 lb of coal (fossilized dried organic matter) to produce what amounts to one ounce of dry organic matter. That's an energy efficiency ratio of 1/60th or 1.7%.
If you happen to have a wind turbine on your property and the electricity isn't otherwise used (and you don't have a grid intertie), there's no harm in using that electricity to grow your own food, or start your own seedlings. But if you're grid connected, or buy your power off the grid, it's probably much better not to use any form of grow light, from an environmental perspective.
Of course, that's not the only criteria. If you're determined to grow heritage plants, for instance, and you don't have a local greenhouse that grows them (using natural light), you may want to start seedlings yourself, using LED growing lights to supplement a daylight source for a few hours a day. And if you live so far from the nearest available lettuce that you'd have to make an extra trip in your car to buy a head of lettuce, it might make sense to burn the equivalent of five pounds worth of coal energy in your LED growing lights to avoid the drive. But since this website is dedicated to helping people make energy efficient choices, it's important to point out here, that the best way of being energy efficient is to reduce your use of energy.
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