Would a motor run capacitor of the same MFD rating be suitable for a lamp? the reason i ask is because im about to make an order on amazon soon and one of the things i'm thinking of buying is a new cap for that fixture that had failed:

http://www.lighting-gallery.net/index.php?topic=5642.0

But from the looks of it they're all motor run capacitors. are they safe for a lamp? are they going to violently fail or something?

https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=22.5Mfd+capacitor

After the ballast (as in CWA) is fine. Directly across the line voltage (as PFC) - That requires a capacitor specifically rated for such use, or else it might not last long

Use only film capacitor (dry or oil filled), none of the non polar electrolitics that are used in house appliances (they dont last long, they put them in appliances that are not powered up for long time)

If you can get a capacitor with higher voltage rating thats good, as it will improve the reliability to great extent

For a CWA ballast I would highly suggest a Cap specifically made for HID. Motor run seem to heat up with HID.

And keep the tolerance under or equal to 5% of what is needed.

I never had any problems with motor run caps
On Hid ballast . First i dont buy cheap caps
Or even use GE caps, GE caps is known to fail
In street lights.  Puffed up cans.  If you going use motor run cap use 440 volt Am-Rad caps of closest value. They are usually over on plus side of there tolerences. I never had any problems and u are supporting american workers too.

Well, there is huge difference between "motor run" vs "motor start" capacitors, but many people mix those together.
The "start" are supposed to be connected only for few seconds for the motor to start and then disconnected (all that by a starter relay and/or at least a PTC). The reason for this setup is, the low duty ratio intermittent loading allows the use of capacitors, that do not posses as high quality factor (so would overheat when loaded long term; e.g. bipolar electrolytic) or very high loaded dielectric film capacitors.
As a consequence, these capacitors can not endure longer term loading, so are not suitable for anything but some starting applications.
This concept is used mainly or higher power motors and in applications without that much frequent starts, but with long run periods. The main advantage is, the capacitor does not wear out during the motor operation, so the system becomes more reliable and longer lasting.

On the other hand the "motor run" capacitors are intended to be connected permanently to the motor, so loaded all the time the motor is running. The drawback is, they are larger, more expensive, but mainly wear all the time the motor is running. The primary use is for applications with either lower power (too high for shielded pole type, but too low to justify the complexity and cost of starting capacitor switching system - the larger run style is still cheaper) and for applications with frequent starts and not so much runtime (so where the start capacitors would wear too much as well, while the degradation of the run type is not yet a problem; the life rating uses to be around 10khour).
These capacitors then could be used for lighting (it is the same type of load as they are designed for)

But there is still difference between the motor run vs lighting capacitor: The lighting type usually features longer operation life rating (100khours or so).
But with many real life components the life rating is published as a function of the applied voltage, so one component may serve as a 500VAC motor start (rated life in the order of 1000hours/500VAC), 350VAC motor run (rated life in the order of 10khours/350VAC) and/or a 275VAC lighting (rated life around 100khours/275VAC) capacitor.
And similar life reduction/extension could be expected with practically all capacitors rated for permanent load, so any motor run rated capacitor may well become reasonably lasting lighting capacitor (with life expectancy of 100khours or so), if the operating voltage load is kept below 70% of the "motor run" voltage rating.

But such extension does not automatically apply for the motor start type: These could use the electrolytic concept and that means they can not be stressed for longer than few seconds practically regardess of the used voltage - they will just overheat and explode (or vent; in both cases it means their death)...

Well, there is huge difference between "motor run" vs "motor start" capacitors, but many people mix those together.
The "start" are supposed to be connected only for few seconds for the motor to start and then disconnected (all that by a starter relay and/or at least a PTC). The reason for this setup is, the low duty ratio intermittent loading allows the use of capacitors, that do not posses as high quality factor (so would overheat when loaded long term; e.g. bipolar electrolytic) or very high loaded dielectric film capacitors.
As a consequence, these capacitors can not endure longer term loading, so are not suitable for anything but some starting applications.
This concept is used mainly or higher power motors and in applications without that much frequent starts, but with long run periods. The main advantage is, the capacitor does not wear out during the motor operation, so the system becomes more reliable and longer lasting.

On the other hand the "motor run" capacitors are intended to be connected permanently to the motor, so loaded all the time the motor is running. The drawback is, they are larger, more expensive, but mainly wear all the time the motor is running. The primary use is for applications with either lower power (too high for shielded pole type, but too low to justify the complexity and cost of starting capacitor switching system - the larger run style is still cheaper) and for applications with frequent starts and not so much runtime (so where the start capacitors would wear too much as well, while the degradation of the run type is not yet a problem; the life rating uses to be around 10khour).
These capacitors then could be used for lighting (it is the same type of load as they are designed for)

But there is still difference between the motor run vs lighting capacitor: The lighting type usually features longer operation life rating (100khours or so).
But with many real life components the life rating is published as a function of the applied voltage, so one component may serve as a 500VAC motor start (rated life in the order of 1000hours/500VAC), 350VAC motor run (rated life in the order of 10khours/350VAC) and/or a 275VAC lighting (rated life around 100khours/275VAC) capacitor.
And similar life reduction/extension could be expected with practically all capacitors rated for permanent load, so any motor run rated capacitor may well become reasonably lasting lighting capacitor (with life expectancy of 100khours or so), if the operating voltage load is kept below 70% of the "motor run" voltage rating.

But such extension does not automatically apply for the motor start type: These could use the electrolytic concept and that means they can not be stressed for longer than few seconds practically regardess of the used voltage - they will just overheat and explode (or vent; in both cases it means their death)...

very interesting incite