I have two fluroescent plant stands that are on timers. During this last week, neither has lit. They way I get them lit–believe it or not–is to touch the bulb or even just let my hands float near it (after the current has been on a while, to be sure). That both of them stopped at the same time seems too much of a coincidence. The only thing I can think of is that every morning this week the humidity has been in the high 90% range. Could this have affected the choke in some way? Any thoughts or suggestions?
Bad starters or ballasts, maybe.
We have the same problem with the florescents in our bathroom. After someone has taken a shower, or in the summer when it’s quite humid, you have to gently stroke or touch the tube to get them to start. I’ve experimented–you can leave them on for a long time, but they won’t light up until you touch them–and they always light right up with the first stroke.
Are your bulbs dark at the ends? If so, they are burnt out. Even if they still light, a bulb in that condition puts out only half the light it should. For your plants, this means slow growth. In Podkayne’s bathroom, it could mean shaving cuts.
By the way, Hari Seldon, the light distribution from a flourescent tube is not at all even. It’s strongest at the middle, and falls off in a bell curve except for a bulge at each end. It also falls off dramatically as you get further from the tube itself. Your best plant growth will come from getting the plants as close to the tube as possible. The tube is relatively cool, but direct contact with the tube will cause leaves to go brown. Keep the tubes clean; dust can cut light intensity by up to 30%.
This is a common problem with some fixtures which require the metal reflector to be grounded. If it is not grounded the tubes have trouble starting but if you touch them they will start. I believe the distance between the grounded shield and the tube has to be less then 1/2" .
The tubes are not dark at the end. The plug is a grounded plug and it was rather hard to find a three prong timer, this one is, although I have never tested to see if it works. Somewhere I have an ohmmeter, although it probably needs a battery.
I do place the tubes as close to the plants as possible. Actually, almost all the plants are outside for the summer, but I am concerned for the fall.
Any source of light falls off as the square of the distance; there is nothing special about fluorescents on this score. The thing was that both fixtures started doing it at the same time and this coincided with the extraordinary high humidity we have been having. Is that post hoc reasoning or a real effect? From Podkayne’s experience it might be a real effect. Fortunately, I don’t shave under fluorescents–or at all.
Eh? No, I don’t think so. I’ve never seen a fluorescent fixture with grounded plug, and even if there were, it would have nothing to do with the tubes igniting or not. The starter circuit is just a switch to turn on the filaments to vaporize the mercury. The problem in the OP sounds more like a ballast problem. Touching an energized fluorescent tube creates a shunt for current to flow, apparently just enough to start the ioniziation process in this case. You can see this effect clearly if you energize one side of a tube with a high voltage of a few kV. Touching the tube it will glow bright from the energized end up to where you touch it.
Iwant to clarify that I am not suggesting there are no fluorescent fixtures with grounded plugs. There certainly are, I’ve just never seen one, that I can recall.
Sorry Q.E.D., but you’re incorrect.
Some fluorescent fixtures do require the reflector to be connected to earth ground in order to properly start:
http://www.repairfaq.org/REPAIR/F_flamp.html#wgf
Sailor and I are not saying this is the problem; we’re saying that this could be the problem…
Well, whaddaya know? Learn something new everday. Thanks, C_M.
Basically there are three types of fluorescent lamps: pre-heat, rapid start and instant start. Pre-heat have starters. Rapid start requires a grounded plate near the tube as an aid to reliable starting.
This fixture has no starter I can see. I will eventually take it apart and see what’s inside, but it seems to me that I have seen them with the starter (small metal encased tube, right?) exposed for easy replacement. Does that help identify what kind it is? And it certainly has a grounding plug. There is no sign on it that suggests that the grounding is there for anything except safety, however. No signs at all, in fact. It just sits there. And the reflector is just a hair over 1/4" from the tubes. I really have to find out if it is really grounded. All I know is that the socket is relatively recent; the timer has a three pronged outlet and everything looks right.