Question: I’ve been growing my African violets under lights. I’m expanding my growing space and am wondering if I can simply double the number of florescent lights if I double the width of my shelves–i.e. if I have one tube for 20″ wide shelf, can I use 2 for a wider shelf.
Answer: Assuming you don’t change the type of bulb, yes. Nowadays, though, not all bulbs are the same and it’s become more complicated. Over time, we’ve replaced most of our T12 fixtures with those using more energy efficient T8 bulbs which, as a rule, are much brighter. We’ve actually found that we can get away with using only one T8 bulb for many varieties (we simply unscrew one of the two bulbs in the fixture), we we had used two T12 bulbs. Whatever the bulbs, try using fixtures with solid-state (not magnetic) ballasts. This will save you on electricity use and will produce far less heat. This can be significant if you have more than a few lights, especially in summer, when heat can be an issue.
Shopping for lights has gotten more complicated. There are dozens of different sizes and types, and each will produce different amounts of light. Look for the light output (lumens) on the label–there can be significant differences between bulbs. ‘Color temperature’ (i.e. 5000k, for example) will also be listed. In our experience, this is of less importance (though higher is generally better). LED bulbs are the present day choice. We use a four foot, 10 watt fixture. Full spectrum is best, but not critical.
Whatever you decide to use, let your plants decide what is best. If your violets look healthy, have good color and bloom, then all is well. If they bloom, but new growth is crowded and leaves are off-color, it may be too bright. If the color is good, but leaves don’t lay flat and blooms are sparse or infrequent, you likely need more light. Adjust bulbs, distance from bulbs, hours of light, and placement of your plants on shelf (center of shelf for more light, outside of shelf for less) until you get the best results