We learned at school (20+ years ago) that the stroboscopic effect was a true problem and cause of injuries (even fatal ones) because rotating/moving parts (wheels, chains) might look still or moving much slower and/or in the opposite direction. The light source in question were magnetically ballasted fluorescents, of course.

Two different solutions were suggested:

• three-phase wiring and three-tube fittings (each tube powered by a different phase)
• two-tube fittings, one tube "delayed" by a capacitor

I wonder if anyone have seen such fittings or if it's just a theory, never accomplished.

Note 1: The first suggestion should work also with three separate LED modules. Not sure about the second one.
Note 2: In our factory hall, we have new LED lighting installed a few months ago and I haven't noticed any flickering there.

Most (or all?) of the North American 2x40 preheat ballasts had one tube delayed by a cap, or, as some manufacturers referred to it, "lead-lag" or "stroboscopic corrected".

The gymnasium (sports hall) at my high school had 16 metal halide lamps of 400 watts each. They were wired two per circuit. They were fed from a 3-phase panel and distributed as evenly as possible (since 8 doesn't divide perfectly by 3) on all 3 phases. If I remember correctly, there was less visible flicker on moving objects when all were lit. When only one or two circuits were lit, the flicker was very pronounced.

I visited a cabaret in France, and talking with the bartender who was cleaning glasses, I could see the flicker very well from the single lamp fixtures under the shelves behind the counter as she was moving the drying cloth around. As a matter of fact, I find that magnetically ballasted lamps on 50Hz have more pronounced flicker than on 60Hz. Same applies to street lighting.

Magnetically ballasted lamps do, in fact, flicker more obviously on 50 Hz than 60 Hz. That is because at 50 Hz, there are fewer on/off cycles per second, so the strobing is more perceptible to the human eye.

Most (or all?) of the North American 2x40 preheat ballasts had one tube delayed by a cap, or, as some manufacturers referred to it, "lead-lag" or "stroboscopic corrected".

That's interesting! I think that magnetically ballasted fixtures here were manufactured just with power factor compensation capacitors and suppression capacitors in starters (AFAIK).
Wikipedia Fluorescent lamp page shows the "beat effect" video (it's almost at the bottom of this page) and both tubes seem to have the same beat - so no stroboscopic correction.

In Europe, I believe it is possible to add a capacitor in series with a ballast to shift the phase and reduce flicker, although it would be special applications only. For reasons I cannot explain, I believe you need a starting compensator in the starter loop to ensure it fires properly. It is simply a small inductor.

This setup would only be used in a two lamp fitting where the other lamp would have a standard choke ballast.

The power factor correction capacitor is separate from this one, and would be added to the entire circuit in a large installation.

Quote from: nicksfans on October 01, 2014, 06:04:30 PM

Most (or all?) of the North American 2x40 preheat ballasts had one tube delayed by a cap, or, as some manufacturers referred to it, "lead-lag" or "stroboscopic corrected".

That's interesting! I think that magnetically ballasted fixtures here were manufactured just with power factor compensation capacitors and suppression capacitors in starters (AFAIK).
Wikipedia Fluorescent lamp page shows the "beat effect" video (it's almost at the bottom of this page) and both tubes seem to have the same beat - so no stroboscopic correction.

In Europe, just the series inductor ballasts are nearly everywhere, mainly because they are very simple. So there the high power factorpower factor is indeed just the capacitor parallel to the mains.

In the US, way more variety of ballasts are in use, as the 120V does not allow that simple series choke for a longer lamp.
Most ballasts were of the RS type, because the 120V needs a transformer anyway, so adding the extra filament windings was cheaper than the starter and it's accessories.
Cheap ballasts for domestic use (NPF) just the high leakage autotreansformers, just because there was nothing else necessary. These ballasts were lag only and usually supplied the lamp by way lower than rated wattage (at home, such high output as from 40W lamp was not necessary, but it was a benefit to use that most common lamp type, because it was cheap). Because of the main use, there was no need to compensate the power factor there. Because mainly single lamp, it had the 120Hz flicker.

The commercial use units used full lamp power (because the light output was really needed) and it was arranged so, the power factor was corrected before reaching the primary winding. SO it was either lead style ballast with an air gap in the transformer core (so it's low main inductance then compensated the power factor of the capacitive load), mainly used with ballasts either for single lamp or two in series.
This was lead only, so no 120Hz flicker reduction (just the end 60Hz flicker in the electrode area was suppressed by having the current flowing in each tube in the opposite directions)

And then some were lead-lag. Mostly the four lamp units (two series pairs), and some two lamp ballasts. It was a bit more complex core than for the plain series combination (the lead-lag requires three sections separated by the magnetic shunts: Primary and two secondaries), allows independent operation of each branch and partially suppresses the 120Hz flicker.

So if the ballast is designed to be high power factor on it's own, so no separate power factor correction.

And then of course the high frequency ballasts took over on both sides of the pond...

We had lead lag fittings in part of the factory where I worked they were quick start fittings with a cap in series with one tube and its choke and the other tube just had the choke. These were run on normal 250 volt mains

Easiest way is to use electronic ballasts with a good regulation. Some are horrible and have consideration power frequency modulation passing through, but many have less flicker than an incandescent.