Starters for fluorescent tubes come in many different types which can be confusing. They are often called starter motors or ignitors as they essentially start the tube
There are two main types to choose from – electronic and conventional
The advantages of an electronic starter switch is they “soft start ” which extends the life of the tubes, they reduce flickering and will help reduce tube failure because they simply stop the tube rather than let it strobe. Electronic starters will also work with any length tube so it means it is easy to get it right!
Ordinary tube light starters are specific to certain lengths so you must select the right one for your tube otherwise it wont work properly
For 2 ft tubes in multi tube fittings you need a series starter which usually goes by the code FS2. This is because the lamps share a ballast
Up to a 5 ft tube an FSU starter is required, this is probably the most common one
Above 5 ft you need an FS125