Many gardeners use fluorescent lamps to light their plants, especially their seedlings. They are much more efficient and durable than incandescent lamps (and don’t burn tender seedlings!), but less so than newer (and, in my opinion, still too expensive) LED lamps. But the question every light gardener eventually has to ask is: when is it time to change the tubes?
Most manufacturers claim their tubes last 7,500 to 15,000 hours (compare that to 500 to 1,000 hours for an incandescent bulb). I’d say, from personal experience, you can certainly expect at least 10,000 hours of use before a tube actually stops working.
That said, fluorescent tubes gradually lose their effectiveness over time. Yes, they light up and their light may seem nearly as intense as ever to human eyes, but plants, which depend on these tubes for their survival, aren’t fooled. When the tube approaches the end of its useful life, the plants growing under it can start to suffer from a lack of light.
The Basic Rule
The calculation used by generations of gardeners (and fluorescent lamps have been used in horticulture since the 1930s) is that, at 12 to 14 hours of use per day, fluorescent tubes are good for about two years. After this period, their effectiveness begins to seriously diminish. So, logically, you should replace them every two years … if you use them year-round.
If you only use them for starting seedlings in the spring, so for about three months a year, you can multiply that number by four. They should therefore be good for eight years. (But do run a damp cloth over the tubes each spring to remove dirt and dust.)
However, even if you exceed those limits, as long as the tube lights up (eventually, any tube will burn out and simply stop lighting), it can still be used to light plants, but you might need to move your seedlings closer to the lamp or use it for plants that tolerate weaker light.
One Down, One to Go
Note that when a two-tube lamp stops lighting, probably only one of the tubes has actually burned out. Often, it’s the tube that is blackest at the ends. Try to replace that one with a fresh tube. If the lamp doesn’t light up, put the first old tube back in and try replacing the other. Both should then light up. If nothing happens, it’s likely that the lamp’s ballast has stopped working (not a common occurrence, but it does happen). If so, sorry, but you’ll have to replace it.
Managing Plant Lights: My Story
How do I, as a laidback gardener, manage my fluorescent lights? And I have lots of them: some 30 lamps all over the house.
I’m definitely a procrastinator and besides, how can I remember when I replaced this or that tube … especially seven or eight years later? Quite honestly, I simply wait for the tube to darken at both ends before replacing it, a very clear sign that the tube has lost its effectiveness. Experts would probably say that that I’ve waited too long, that by the time the ends darken, the tubes have been seriously inefficient for quite a while, but what can I say? That’s what I do!
Now, you need to realize that when I garden under lights, it’s for my own personal use: sowing vegetables and annuals, starting cuttings, growing indoor plants of all kinds, maintaining terrariums, etc. I’m sure that if I grew plants as a business, I’d pay much more attention to their efficiency (there are light meters you could use to determine a given lamp’s light intensity, for example). But the “darkened tube ends” method works for me … and I’ve been growing plants that way for 40 years now.
But you decide: how you handle your light gardens is up to you!
Correctly Disposing of Fluorescent Tubes
When you do decide to replace fluorescent tubes, don’t forget to bring the used tubes to an authorized drop-off point. There is probably a recycling center not far from where you live or, if not, many hardware stores have a bin where you can deposit your used tubes. This is important, because fluorescent tubes do contain some mercury and need special handling at the end of their useful life.