This only happens during the summer months, as it is the third summer in a row, but when it is hot outside, my overhead flourescent fixtures takes anywhere from 15 minutes to 1 hour to come on.  It's twin comes on immediately, but for some reason during the summer, one of the fixtures acts up.  I have tried changing the lamps, but does this sound like a ballast problem, or a starter problem?  Would pics help (I doubt it).  But I don't know much about flourescent luminaires.  My area of amateurise lies in HID lighting, and I'm not even as skilled as a lot of the members on this board at HID either.  All I do is collect them, and with the help of you find gentlemen and ladies among us here, fix them. 

Preheat ? Old ballast with cloth wiring ? Maybe isolation breakdown somewhere that clamps down the starter pulses, so the lamp never sees appropriate voltage for starting

Is it Earthed ? (whether by Earth wire, or by being hanged on chains from a metal ceiling beam)

Is it and the circuit it goes to wired correctly ? (Neutral used for Neutral, Earth used for Earth)

Test resistance between all ballast outputs and lantern metal

Test current on lantern Earth wire when connected to AC power and trying to start (for example : Wire the Earth through a resistor like a low power Incandescent lamp, and measure voltage across the lamp



Does the ballast contain a capacitor ?

Would the lantern have the same bad behavior in the winter, if you switch it on and let it warm up for a few minutes..15 min, then while the ballast is still hot, replace the lamps to cold lamps and try again to start it ?

If yes, the capacitor may be acting up and showing its bad behavior only when its hot (but if the lamps are hot too then they are easier to start, and that hides the bad behavior of the ballast in the winter)

If they are rapid start magnetic F40, they can be hard starters in humid weather. The accumulation of dirt on the surface of the lamps and reflector/channel cover combined with the humidity can reduce the capacitance required for reliable ignition. You could try cleaning both the lamps and the reflector to see if things improve. I'm not implying your fixtures are dirty, but you know, it only takes a small amount of dust to cause a nuisance. Otherwise, maybe preheat ballasts would behave better... If not, try finding ballasts with a higher OCV.

Or, provided your ballasts are rated for them (big IF), try 34 watt energy-saver lamps, they sometimes start better in the above conditions, but are also very cold-natured.  Where is the offending fixture, is it a heated place in winter?

Preheat ? Old ballast with cloth wiring ? Maybe isolation breakdown somewhere that clamps down the starter pulses, so the lamp never sees appropriate voltage for starting

Is it Earthed ? (whether by Earth wire, or by being hanged on chains from a metal ceiling beam)

Is it and the circuit it goes to wired correctly ? (Neutral used for Neutral, Earth used for Earth)

Test resistance between all ballast outputs and lantern metal

Test current on lantern Earth wire when connected to AC power and trying to start (for example : Wire the Earth through a resistor like a low power Incandescent lamp, and measure voltage across the lamp



Does the ballast contain a capacitor ?

Would the lantern have the same bad behavior in the winter, if you switch it on and let it warm up for a few minutes..15 min, then while the ballast is still hot, replace the lamps to cold lamps and try again to start it ?

If yes, the capacitor may be acting up and showing its bad behavior only when its hot (but if the lamps are hot too then they are easier to start, and that hides the bad behavior of the ballast in the winter)

In the winter, they have no trouble igniting.  Yes, it is in a climate controlled room, so in the winter it does ignite properly.  It does appear that it acts up only when it is hot and humid outside.  I need to get up there and take a look at the ballast.  Then I can let you know if there is a capacitor there, and what kind of ballast it is.

Wipe down the reflector/channel cover, and also wipe the lamps thoroughly with a damp cloth and then dry them before reinstalling them in the fixture. Also, make sure the fixture is grounded. If it still doesn't work right, grab some bare light-gauge wire and wrap it around the lamps, and then connect the wire to something grounded (like the casing of the fixture). If it still doesn't work, your ballast is probably losing OCV due to a bad cap and needs to be replaced.

Could it be under voltage supply when aircon is on??

The ballast type can be determined from the starting behavior. Rapid Start fades in, Preheat flashes and sometimes makes matching sounds while at that

The ballast type can be determined from the starting behavior. Rapid Start fades in, Preheat flashes and sometimes makes matching sounds while at that

They are Rapid Start

With RS check everything that was said above

In addition, measure OCV, cathode heating (are the lamp ends becoming hot even when the lamp is not starting ?), and Earthing of the lantern metal

Try to replace with tested good lamps

Try to swap Phase and Neutral (Black and White) on the ballast inputs

If the ballast contains a capacitor (most of them do in the US ?) the capacitor may be failing. This is possible to repair only by opening the ballast and replacing the capacitor - which is quite a project with tar filed ballasts

Residential-grade RS ballasts typically do not contain capacitors, but it's not uncommon to see HPF ballasts in residential installations,  and those do have capacitors. A weak cap can cause low OCV and unreliable starting. Its not really worth it to replace a cap... You should just replace the ballast.

I would guess for some connection problem, when the things become heated, it starts to act.

Or other possibility could be a humidity: In the warm months the absolute water content in the atmosphere increases, so when the lamp is sometimes exposed to cold temperatures (at night; I would say quite common for deserts like Arizona/Utah or so, as far as I remember being there; mainly early mornings), it may easily become the coldest thing all around, so the water may condense on it, making then the starting more difficult.

At one of my church buildings- quite a few fixtures that had the T12 Rapid Start Mag ballasts would not light up when turned on after a summer rain/thunder storm.  If I turned the switch off and on several times at different intervals, the lights would all come back on.  if I left the switch on, the fixture would come on after 3-5 minutes or so.  I suspected a grounding issue, or something to do with the humidity because this only happened in the summer after a storm.  Ballasts didn't have a ton of life on them, maybe 8 hours every Sunday since 1973 and 1-2 hours during the week up to the time I converted over to T8.  I saved a few of the ballasts.  Universal brand. 

At one of my church buildings- quite a few fixtures that had the T12 Rapid Start Mag ballasts would not light up when turned on after a summer rain/thunder storm.  If I turned the switch off and on several times at different intervals, the lights would all come back on.  if I left the switch on, the fixture would come on after 3-5 minutes or so.  I suspected a grounding issue, or something to do with the humidity because this only happened in the summer after a storm.  Ballasts didn't have a ton of life on them, maybe 8 hours every Sunday since 1973 and 1-2 hours during the week up to the time I converted over to T8.  I saved a few of the ballasts.  Universal brand. 

This is what happens with both of mine.  The second one only started failing this year.  It doesn't have to storm, just high humidity outside and heat.  When it is low humidity/cold outside, it doesn't matter jow warm it is inside, they start right up.  I may just replace the ballasts.

Are there ones without capacitor that are failing the same way ?

Can a failing ballast then be used for 1 lamp, sorta in a same circuit as would be with the "shorting energy saver tube" ?