Fluorescents hard to light

I have two adjacent ceiling fixtures holding two 40W 48" fluorescent tubes, both controlled by a wall switch. Sometimes, they go on properly; other times they'll go on if their glass tubes are touched; still other times they need to be rotated slightly in their sockets. And sometimes they won't go on at all.
What should I check?
The fixtures are at least 18 years old, but do not have the little starter cans that older fixtures used to.
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Are the metal fixtures attached to the ground wire (green one) WW
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Even if the fixtures are properly gounded, if there is a thin film of dirt on the tubes, it can be so thin it is invisible, that film may keep the bulbs from lighting. Especially if the humidity is high.
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If the bulbs are old, try replacing them. or just replace the ballasts with electronic 2 light 32 watt units, and matching bulbs. They will start instantly
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Seems common to me. Mostly due to sockets. They often fall apart.
Greg
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On 5/19/2011 3:40 PM, Ivan wrote:

At what temperature do the bulbs act up?
TDD
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Ivan wrote:

Flakey fixtures, such as you describe, are often traced to a problematic ground connection. The ground for a florescent fixture, unlike its use for most other electrical devices, is a necessary component of the device in creating a flux this close to the galactic core - or something like that.
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It starts the arc from one end of the 4' tube toward the other end by initially arcing from the "hot" side of the ballast output toward the "ground" of the metal fixture, and the arc progresses down the tube until it stikes fully. That is why a greasy film on the outside of the tube will sometimes inhibit the initial arc from stiking, in effect it insulates the tube from the "ground".
This is a generalization/simplification, but is how it really works
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On 5/19/2011 3:40 PM, Ivan wrote:

i'd be checking the ground to the fixture(s)
--
Steve Barker
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