I have one fluorescent tube in my kitchen that does not always light up when switch is turned on but all the others do. Funny thing is, if I just barely touch the light with my finger, on it comes. What causes this? Direct ends on the tube? Thanks for any info.

 

Swap the positions of the tubes and see if the problem travels with the tube. If you have multiple fixtures you can also swap to a different fixture.

 

Sounds like the fixture needs to be grounded.

 

Like OP, I've often wondered about this too. I've experienced it in several homes I've lived in over the years. Presently, I have a 4' shop light in the garage that's started refusing to come on during humid conditions (rainy outside), where just barely touching either tube anywhere along their length instantly lights them up.
Tubes were replaced several years ago and are not discolored at their ends, but the fixture and ballast go back to 1985 when the house was built. I'm sure that replacing the ballast would probably solve the problem, (not really a problem, just touch the bulb), but was wondering what causes this. (Fixture is properly grounded, as measured by VOM).

 

Tubes are F40CW Philips, if it matters.

 

Years ago fluorescent tubes had a lot of mercury in them. When the filaments were heated the mercury allowed for fast ignition. You could figure on fairly long life.

Today.... the level of mercury has been slashed due to all these tubes ending up in landfills causing a mercury disaster. It now takes a higher voltage to be able to start the arc. The high voltage will arc to the shortest path and that would be ground.... a grounded fixture case.... or your hand.

T-12 tubes are dead. Switch over to new electronic ballasts with T-8 lamps. Longer life with less energy use. The T-8's will fit in T-12 sockets.

 

Or go to LED retrofit tubes. No ballasts needed, lower operating costs. On places like Amazon you can get the LEDs at about the same cost as a new T8 ballast and T8 tubes.

 

Careful there. Not all T-12 fixture will work with T-8 bulbs. Depends on the internals.

 

To use the new LED style, do you just bypass the ballasts and wire directly to bulbs?

 

It depends on the LED replacements you buy. Some are plug and play and will run of an existing ballast, (if compatible with the ballast) while others bypass the ballast and run off of 120 volts. You will get the most energy savings if you use the ones that bypass the ballast.

 

On LEDs you also have to watch if both power wires go to the same end or one to each end. Some T-8 tombstones are internally shorted and won't wok with ones where both power leads go to the same ends. Ones that have one power lead to each end will work with either type of tombstones. Note T-12 tombstones as far as I know are never internally shorted.

 

Thank you gentlemen, in my case, since the tubes are only a few years old, and the fixture doesn't get much use (probably why 1985 ballast still works), and assuming a new T-12 compatible ballast (they're a lot smaller now, I noticed) would operate the tubes more efficiently, should a new ballast not give me several more years operation?

 

rstripe if you can still find T-12 tubes then a new ballast that would operate T-12 tubes would be in order. If however you can't find them at all then I would do as PJmax suggests or as Ray2047 suggests and buy either new fluorescent tubes or buy the more energy efficient LED tubes. The best LED tubes as has been mentioned are the ones without the need for a ballast. The ballast free tubes can be a bit tricky to install but once up there in your fixture they give off fantastic light and use a great deal less electricity.

 

I believe they were only referring to the tombstones being the same spacing, not necessarily the ballast.

 

Can you install a new electronic ballast for T-12 tubes..... certainly.
Electronic Ballast for 4 ft. 2-Lamp T12 Fixture-GE240RES120-DIYB - Home Depot

Does it make sense ?
No.... not really because when those tubes go bad you'll need to update again.

 

Thanks for the link, PJ. As far as T-12 availability, all the big box stores and neighborhood hardware stores around here still have the popular sizes. My replacement reasoning was that if the original tubes lasted 25 years and the "new" ones are only 4 or 5 years old and give good light, that a new (more efficient?) ballast would extend these tubes another 20 years plus, and solve the problem of having to touch them when it's humid.

 

Hey it's another one of the fluorescent light doesn't start without touching it threads. Rapid start has a design flaw where it doesn't start if the fixture isn't grounded, or if it's too cold, or too humid, or simply doesn't feel like it. If starting is unreliable, make sure the fixtures are grounded as previously suggested. If grounding is not enough, run a thin strip of foil tape along the length of the tube (facing the reflector) and stop about an inch or two from the ends. If you've ever worked with the 34W T12 U-Bend lamps, some of them have a starting strip like this built-in (U lamps are tough to start).

Newer electronic ballasts (or the older preheat type) don't have this issue at all. The foil solution is the cheapest and in at least my limited experience, always works provided the tubes are good and the reflector is actually grounded. If you try it, just be careful it doesn't make electrical contact. If you ever see unreliable starting combined with one end of a tube darkening quickly (with a new lamp), then you're issue is missing cathode heating current, which is usually a result of a bad ballast or poor connection at the lampholder.