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?
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.
