If I am wanting to run North American lighting that is not frequency dependent in a 220-240v 50hz country, is it safe to make a DIY voltage converter that uses a 120v light bulb in series with an outlet if I want to run a North American light bulb or fixture with North American 120v mains voltage bulbs or 120v ballasts?

When you are using a resistive dropper you really are limiting the current but not the voltage, so it will become sketchy if you want to power up anything else than a resistive load of around the same power. If the load is high you will measure low voltage between the lamp output and neutral, if the load is low or there is an open circuit you will measure full mains, and that effect becomes stronger because the resistance of the incandescent lamp variates with the temperature. At low loads the filament will run cold allowing more current to pass. So you just gotta be careful with that.

Tungsten lamps are better thought of as PTC resistors. You seem to want to think of them as 120V zeners or something but they're not. They do nothing to change the voltage directly.

Use an autotransformer. They are simple, reliable, and cheap.

Tungsten lamps are better thought of as PTC resistors. You seem to want to think of them as 120V zeners or something but they're not. They do nothing to change the voltage directly.

Use an autotransformer. They are simple, reliable, and cheap.

From what I understand, 2 120v incandescents seem to operate satisfactorily in a series pair on a 240v mains supply, I wonder if it is safe to run 2 identical 120v 60hz lamp/ballast setups in series on a 240v 60hz mains supply?

From what I understand, 2 120v incandescents seem to operate satisfactorily in a series pair on a 240v mains supply, I wonder if it is safe to run 2 identical 120v 60hz lamp/ballast setups in series on a 240v 60hz mains supply?

The word "identical" is key here. If there is any difference among them, one of them would see quite significant overvoltage. And the imbalance is just becoming greater and greater as the lamps age...
You should take into account the production variation or even the differences among makers and what the wear causes on them.
So usually you get significantly shorter life, as normally even when with identical rating, they are far from being electrically identical enough.

Use an autotransformer. They are simple, reliable, and cheap.

An autotransformer is the best for such purposes, but they are nothing near to cheap, a basic 500VA one can round 100 bucks, don't know you but that's quite some money. That's why he's looking for an alternative like an incandescent current dropper.

@WorldwideHIDCollectorUSA you might try to add a light dimmer in series with the incandescent lamp, by this way, as well as limiting the current with the bulb you can limit the voltage by cutting part of the phase, so if you set e.g. the dimmer at 50% you get a 120V peak voltage. I only recommend that for resistive loads because an irregular current drawing load like an inductor, capacitor or switching power supply might fry the dimmer.

$100 is well worth it, but there are cheaper DIY options. A variac in many cases for instance. Also, many older appliances have 2 120V windings that allow easy switching between 120V and 240V mains. With a 240V mains, the center point of such a transformer is at 120V potential. Old audio amplifiers often have large transformers that may be suited for this. You can even add an array of old assorted regular low voltage transformers in series in a buck configuration to get your voltage down. Buy used. Look around. Thrift sales. Whatever the EU equivalent of craigslist. It doesn't need to be an off-the-shelf brand-new bespoke artisan grass-fed transformer, you know.

Sorry if that's too much work, but if $100 is too much (and I've been there before), you need to get creative.