I always had trouble when buying a capacitor because it said they were either for washing machine, tumble dryer or for motor appliances.

If I was to connect a SOX bulb with these 3 options, would it work probably or do I need a specific one for bulbs?

You have to study the datasheet
For capacitors the important parameters are the capacitance and its tolerance,
the voltage and temperature rating for a required lifetime. This later uses (at least what is common in European market for generic AC capacitors) to be often published as multiple ratings dependent on the required lifetime and duration how long the capacitor is exposed to the voltage at a time.

There are three types of use so designed lifetime rating:

- "Lighting" with 100+ khour rating, yielding the lowest published voltage and temperature rating figure, intended for applications where the capacitor is connected to the voltage for really long time
- "motor run" with about 10khour lifetime rating stressed for the time a power tool like equipment is operating in use
- "motor start" with about few 10's hour rating, intended only for very brief intermittent operation (few seconds to start motors, then disconnected).

So rating of quite common AC capacitors uses to be 550VAC for "motor start", 450v for "motor run" or 350V for "lighting".

For film capacitors (the paper-in-oil belongs here) this is the typical ratio (when the TDDB is the dominant wear mechanism), so if you happen to have a "400VAC motor run" rated capacitor with no other ratings on it, you may expect it will most likely be usable also for up to 300V for lighting. Using at higher voltages than published is very problematic, as you may trigger another aging/destruction mechanism (hard breakdown,...) which does not follow the TDDB ratios.

And the (bipolar) electrolytic motor start capacitors you can never use where they are connected for longer than a few seconds at a time either, as these are very lossy and would overheat.


And also note the "lighting" vs "motor run" vs "motor start" rating category does not mean they need to be used only in those circuits, but it is more referring to to the use pattern typical for those applications ("lighting" is something nearly permanently ON so it easily accumulates the 100khours runtime, "motor run" corresponds to a power tool use, so with ON for few 10's of minutes and then few hours rest, so the accumulated runtime will be in the few khour ballpark, "motor start" means just barely few second connection and then long time cool down while disconnected).
So if you have a worklight used only for half an hour here and there, it would suffice with a "motor run" rated capacitor. Or a fan permanently turned ON would require a "lighting" capacitor rating, just because how many hours it will accumulate, even when the real task is to run the motor.
It is valid also for the "motor start", but there I have no idea what other use would expose the capacitor to the voltage just for few seconds than reallyto start an induction motor on a single phase feed.

Medved tends to over-complicate things a bit here.

First, you have to answer a couple of questions:

- Is it for a long-time installation or just to light up a lamp a couple of times for fun?
- What part of circuit this capacitor is intended to? May be a resonant part or just a PFC across the input line.

For a quick try, almost any film capacitor will do. You have to respect the voltage rating, though. Some capacitors are marked for AC RMS voltage (VAC rating) while some just for peak voltage/DC. This is 1.41 multiplier to VAC. May be confusing. Take care. Getting voltage rating higher than required is of course OK.

Just avoid cheap AC electrolytic capacitors sometimes sold as 'motor start'. These are intended just for a brief operation and have high losses and low precision and probably even will burst if forced to run continuously.

As for a circuit part where the capacitor is used - If this is power factor correction, this is not critical, and capacitor may be even omitted most of the time. For resonant/ballasting part, you should be more careful and select the exact capacitance as ballast manufacturer specified. For hobby use a few brief  times any capacitor is OK assuming capacitance is within a reason (say +-5%) and most of capacitors be they washing machine use or so will fit. For a long time application there is an issue with capacitance loss with cheap (and even not cheap!) dry film capacitors, so you need to look for quality parts, though this is still a gamble. Drifted capacitor will cause lamp current to be off and ballast will start to 'eat' lamps. Of course better to have a good multimeter on hand to verify the capacitance and lamp current.