To grow plants indoors for the plant sync, we had about 150 fluorescent lamps in 75 corded “shop-light” fixtures. Our setup is simply a larger version of what many home gardeners use for germinating seeds or growing indoor plants. Our use of lighting has a substantial cost and carbon footprint, so we are always on the lookout for cheaper and more efficient lighting solutions. For several years, we have had our eye on LED technology, which is rapidly replacing other light sources for many applications. But LED solutions for my plant-based needs were cost-prohibitive, confusing, and not readily available — until 2015.
Shoplight LED fixtures and LED replacement lamps are now available at most big box stores and online. As of June 2016, the fixtures cost about $30-50 and the replacement bulbs about $10.00 each. The upfront cost remains higher than fluorescent fixtures and lamps. However, the LED fixtures use about 25% less energy than equivalent fluorescent products and the lamps last longer. The question is: do they work adequately for hobbyist seed starting? There are many scientific studies in reputable academic journals regarding the comparative performance of various types of lamps for horticulture. However, these studies have not used LED products that are within a reasonable price range or that address the needs of the average seed-starting hobbyist.
We used a Kill a Watt® meter to measure the actual watts used by each fixture. Fixtures were all as advertised, and the LED fixtures indeed provide about a 25% savings in energy use. For the fluorescent fixture two 32W lamps do not = 64W because of a ballast factor. The LED fixtures have no ballast. The fluorescent fixtures used 56W and the LED shoplight fixtures used 41W. For our purposes, relatively inexpensive 48″ LED shoplights now available from big box stores perform at least as well as fluorescent lamps. We have used several brands of fixtures and replacement LED bulbs and they all perform adequately.
As of January 3, 2017 we have successfully used shoplight LED fixtures (not an advertisement) for weekly seed starting in our Heuchera breeding program for 14 months. Heuchera seeds germinate (pictured) in the same time frame and at the same frequency as with my previous experience with fluorescent lamps. Early seedling growth is also at least as good as our experience with fluorescent lamps.
We also did a small experiment with kale seeds.
We happened to have some Heirloom Kale Mixture seed from Seed Savers Exchange. Two pots containing 20 seeds each in a soilless potting mix were placed at a distance of 5 cm under either LED or fluorescent lamps. The LED treatment was supplied by a fixture with LED “chips” purchased from Sam’s Club (specifications; not an endorsement). The fluorescent treatment was supplied in a standard fluorescent fixture with two new T8 6500K lamps (cool white).
For both treatments 18/20 (90%) seeds germinated within one week of sowing (pictured). The appearance and vigor of the seedlings was roughly similar. If anything, the seedlings under LED lamps were more vigorous. The LED treatment is on the right in this picture.
Seedlings were thinned and four individuals from each light treatment were transplanted in 4.5″ pots. The picture below was taken 26d after sowing seed. On the left are kale seedlings grown under LED light. On the right are kale seedlings grown under fluorescent lights.