kitchen strip light

[cgh31]

Hi there, I've got a strip light in the kitchen that is stubbonly refusing to come on properly when I flick the light switch. The ends of the tube light up but not the centre. There is a knob on the side of the strip light which can be twiddled to get the light on but it is driving me mad. What does this knob do and why doesn't the light come on properly? What needs replacing (not the strip light - tried that!) and where can I get it from?
Thanks in advance you wonderful lot!

[Toureman]

The "knob" you keep fiddling with is the starter for the tube, take the starter out and replace with a new one.

Turn it to the left or right and pull out.

[woodchopper]

As said - ends glowing on a fluorescent tube = faulty starter switch - if the ends of the tube itself are severly blackened, best get a new tube as well.