I don't see how hydroponics can be certified organic since organic fertilizers are real no-no's in hydroponics for reasons of sanitation. You don't pump sewage over food-plants. Also, the last time I looked (3 months ago), sodium vapor lamps still give the most bang for the buck, factoring in initial cost. The sodium D lines are a little more energetic than the short IR that chlorophyll likes but they can shrug off the extra energy. I think the blue is just a growth regulator and green is a growth inhibitor since one says the sky is visible and the other says you're being shaded. The price of these LED arrays has plummeted this last year and should soon overtake (undertake?) the plasma type lamps. But who's going to do the heavy lifting on artificial lighting now that everybody's legalizing wacky weed and there's no incentive to grow it in the basement anymore? Tim Eck PA -----Original Message----- From: pbs-bounces@lists.ibiblio.org [mailto:pbs-bounces@lists.ibiblio.org] On Behalf Of Leo A. Martin Sent: Wednesday, February 19, 2014 1:14 PM To: pbs@lists.ibiblio.org Subject: [pbs] Growing under lights I've been doing some reading on indoor lights, for terrestrial plants and planted aquaria. Here is an article I just submitted for the newsletter of the Central Arizona Cactus and Succulent Society. While it understandably focuses on succulents, the information is easily generalizable to bulbs. I have been doing a lot of reading about lights for growing plants indoors. It turns out white fluorescent lights of the proper color are at least as good as specialty "grow-lights." Fluorescent lights, including tubes and CFLs, are sold in different colors of white. They are labeled as to color temperature, which is measured in Kelvins, abbreviated as K. The color temperature is almost always printed on the tube, label or box, often in tiny print. Color temperature refers to the relative proportion of various light wavelengths in the light. When we see multiple wavelengths mixed together they form what we perceive as white light. I discovered years ago that 40 Watt "cool white" fluorescent tubes are fine for sprouting most cactus seedlings and growing them on for a few years, before they are ready to be transplanted outside to individual pots. But "cool white" is around 3,500K, and this doesn't contain enough of the proper wavelengths for most other plants. Cactus seedlings do fine with cool white because they generally don't need that much light to grow. Cool white contains only small amounts of the wavelengths chlorophyll absorbs, but that amount is sufficient for most cactus seedlings for a while. Cool white is not adquate for Opuntia seedlings. The best artificial light color temperature for almost all plants is 6,500K, which is usually called something like "daylight." This has a lot of pink and blue wavelengths, which are the ones absorbed by chlorophyll. Both straight standard fluorescent tubes and CFLs of the proper light temperature and wattage are great for growing plants indoors. Straight fluorescent tubes are now sold in varying lengths and diameters. New small-diameter tubes (T5, T8) are a lot more expensive than the old 1" tubes. The old tubes work just fine at a much lower cost. 4 foot long tubes of 6,500K and 40 Watts can be mounted in cheap 2-tube shop light fixtures and suspended over your growing area. Spiral CFL tubes are engineered to give the greatest amount of light down the axis of the spiral. So, when using them for plant lights, they should not be mounted sideways; they should be pointing down at the plants. Most people who use them as plant lights use individual hanging light fixtures with a conical reflector. A 45 Watt CFL provides as much light as a 200 Watt incandescent light bulb, with much less heat, while using much less electricity. It is possible to bloom high-light plants like Hibiscus indoors in dim rooms under 45W CFL lamps. Use a heavy-duty mechanical clock appliance timer with a 10 to 12 hour on schedule. These are not always available at hardware stores, but they are much more reliable than cheap electronic lamp timers. You may have to go online to find one. Ace Hardware sells heavy-duty mechanical clock timers around Christmas for use with outdoor lights. If you use multiple light fixtures, plug the fixtures into a power strip, then plug the power strip into the heavy-duty timer. Take care the total amperage of your array does not exceed the amperage rating of the timer nor circuit breaker. Many indoor growers have discovered most plants don't need long nights, so plants can have multiple light-on periods per day. I have been told that people who grow certain crops indoors now give their plants 11 hour on, 1 hour off cycles, and they get twice the growth rate - which means half the time to harvest. I haven't tested this with cactus seedlings. Many succulents only open their pores to absorb carbon dioxide at night, storing it until the next day, when they use it to make sugar in the sunlight. Succulents with this kind of metabolism probably shouldn't be on 1-hour night cycles. Cactus seedlings aren't like this; when immature they open their pores during the day, so short nights shouldn't be a problem for them. I have read that adult cacti are limited in the amount of carbon dioxide they can absorb at night, since plant tissues become more and more acidic as the carbon dioxide is stored, and there is a limit to what the plant will tolerate. Cacti taste much more sour just before dawn than they did just after dusk. This is one explanation of why cacti grow slower than plants that can absorb carbon dioxide all day long. Cacti generally have absorbed as much carbon dioxide as they can hold in the first few hours of darkness. So I might guess adult succulents should have somewhere in the range of 4-6 hours of darkness, but this is just a guess, and experimentation would yield real information. Crinkled mylar can be bought very cheaply at hydroponics shops to line reflectors. This provides better light reflection than a pure white or polished metal reflector. Most big-box stores carry 6,500K CFLs, up to and including 45W. If not available at the store they can be bought online. They also carry 6,500K, 40W standard tubes. Most fluorescent tube shop lights sold are 20W so, again, read the label. You have to read the labels and do some searching, because the sales people generally don't know anything about color temperature, and they will try to sell you the much-more-expensive "grow-lights." Tubes and CFLs don't provide the same light output over time; they become dimmer. Our eyes can't tell the difference, but the plants can. Replace straight tubes once a year. I write the date I put them in service on the tube with a marker. For CFLs, read the manufacturer's information on hours of service. Replace the bulbs when they are down to 75% of original brightness, unless you are still happy with your results. Commercial vegetable growers in southern California are now growing organic-certified greens indoors in warehouses under arrays of pink and blue LED lights. Remember, these are the wavelengths chlorophyll absorbs. The photos are eerie because the light looks so strange. The greens are grown in mats on shelves, stacked on wheeled carts, with the LED arrays underneath each shelf, to shine on the plants on the shelf below. There may be 12 or more shelves per cart. Dilute fertilizer solution is pumped to the top shelves, and then flows down to the other shelves. Access is carefully controlled so no insects enter the warehouses, and no pesticides are needed. Leo Martin Phoenix Arizona USA