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Incandescent light bulbs are officially banned in the U.S.
(www.digitaljournal.com)
This is a most excellent place for technology news and articles.
Yeah, that's the problem: PF is not mandatory to be in the packaging so it's not usually there.
If you buy online, sometimes you can find it in the product information section.
I've noticed that the "usual chinese sellers" will mention it if it's good (say, 80%) but not when it's the cheap-converter one (50%).
Alternativelly when looking for the bulbs not likely to flicker you might also look for the "dimmable" ones, as the abiloty for a light lamp to support an external dimmer requirex a better power converter inside the bulb.