i have 1 of those 4ft flourisent light bulb that use with the ballast every once in a while when i turn on the light one of the 2 bulb came on ok the other 1 came on but real dull and flickering like it want to get bright like the other i change both light bulb now both of them does the same thing they come on real pale then it might take aboyt 30 minutes to get bright they are about 1 year old so i dont think it's the ballast is it possible it can be cause by a low voltage or amprage not enough to for the ballast or light

For fluorescent fixtures to work correctly, they need both tubes good and the ballast inside the light to be good. If any of those parts are failing, the light will be flickering & dim, or may not light at all.

So if the light is doing that, one of those parts is failing. Most often it's a tube that is wearing out, so the solution is to replace the tube with one you know is good (like one that is working in another light fixture). If that doesn't fix it, check the other tube (they often wear out at about the same time, since they are always on together).

If both tubes are good (they work in another fixture), then the problem is probably the ballast. In most of those 2-tube lights, it's a little thumb-sized can that plugs into a socket in the fixture. Often this is visible without dis-assembling the light -- it is sticking out under the tubes. Most either pull out, or turn a quarter- or half-turn and then pull out. There are usually markings on them telling the type & size needed, but the easiest is just to take the whole can into the store and tell them you need a replacement for this. Should cost less than $10.

Another possibility (but rare) is that the contacts where the tubes go are corroded, so not making a good electrical connection. Rubbing them with mild sandpaper or a kitchen scratching pad can fix that. But be sure to the light is turned off before doing that! For indoor lights, this is real unlikely, in my experience.