So, there's the circular bulb itself, and also this little removable plastic cylinder with two metal feet on it. How do I tell which of them needs replacing, and what specification to look for to know what to replace it with?
Yeah that's what I ended up doing. Spent way too long in the store staring at the packet like an idiot, because the box said "use with LED replacement starter" but I couldn't figure out if said starter was included in the box or a separate purchase. After about 5 minutes of trying to figure it out I realised I could just open the box and see: yup, it was included.
I don't think they even still sell the fluoro type. The sell the starters aplenty, but not new bulbs.
The cylinder is called a starter, if you google for "halogen lamp starter" you'll find those. Essentially they charge up and then release a spark that ignites the gas inside the actual bulb. They are very inexpensive, so I'd start from there. Doesn't hurt to have a spare anyway.
If you unscrew it, the correct wattage should be written on the bottom between the prongs, just make sure you get one with the same rating so it works with your bulb. Feel free to post a picture of it and I can help search for one.
The prongs itself should be standardized, but the length of the starter may vary, so check if you can still close the lamp.
Essentially they charge up and then release a spark that ignites the gas inside the actual bulb.
IIRC they pull power through the inductor and the electrodes in the tube, so the inductor has plenty of current running through it and the electrodes are hot, then suddenly break that circuit. The inductor makes the voltage across the tube spike super high and an arc forms inside the tube.
The little cylinder is the switch and capacitor at the bottom of the image. It starts off closed, so power goes through the tube's electrodes but not across the tube, then opens forcing power to go through the tube.
It's the rectangular bit that actually does the charging up.
Ah thanks! Frustratingly, Bunnings closes early on Saturdays, so I'll have to wait until tomorrow to actually go out and buy anything.
I think the last time it failed I bought a pack of two starters, and I managed to track down what I think is the second one that came with that (otherwise, it's the old old starter that I never threw away...) and put that in. It doesn't seem to have helped. I also noticed, which doesn't come across well in the posted photo, parts of the bulb are noticeably dark. Is that a good sign it might be burnt out?
Yeah the dark patches on the tube are a sign that it's failed. If you get a replacement tube it would be worth trying it with the original starter (swap them back) to see if it still works.
Otherwise, wattage/lumens, colour and size are the main considerations. There are two sizes of the circular bulbs from memory? They generally come in cool white as well.
Your ballast might also have a max watt rating which would be written on there, but if you get an identical tube it shouldn't matter.
Depending on your situation you could consider an LED equivalent like this one. I recently changed mine after the ballast casing fell apart (it was really old) but I had to get a sparky out to rewire it. The upsides are slightly lower power consumption, LEDs last longer, instant on instead of flickering, and no need for a fluoro starter.
I would take both the fluoro tube out and the starter and just go to Bunnings with them and get them to help pick the right replacements. They stock these in multiple sizes.
If the lamp is flickering, like trying to ignite, but doesn't quite, its usually the starter. As the other post states, it's the cylinder thing. The cream thing is probably just the wiring bridge, which isn't involved aside from providing a connectionnto the mains. The white metal thingy is the ballast, doesn't usually need replacing. As LEDs replace the fluorescent tubes, you will find it harder to find parts, so you might just want to replace the whole fixture with something led based.