Replacement fluorescent tube

[tootsbaloots]

I am looking for a replacement tube for my under cupboard lighting in my kitchen. It is a 550mm 20 W T4 12 diameter. I can't seem to find one that is both 550mm and 12 diameter. I would be grateful if anyone could help me. My kitchen was only fitted in February and although the firm I got it from can provide the tubes at the moment I am worried that I will not be able to just go out and buy one in the future.

[annie0000]

I don't tend to bother what width the tube is, I just get them the right length and wattage. Not sure if this is right or not, but I haven't had any bother. I just get them from Tesco.