Originally Posted by tkrussell
They get dimmer and they can flicker or blink until finally failing to light at all.
What we call a "good burn" for a flourescent lamp, is one that has lived it's normal life, based on published hours of operation, and is that BOTH ends of the lamp are blackened, or grayed with burn rings.
Any flourescent lamp that has failed and is blackened only on one end, is an indication that the ballast is failing, but continues to operate the lamps.
Many times lamps with one black end is just replaced, because this characteristic of lamps and ballasts is not well known, the new lamp will fail in a month or so, and the whole process starts over again, until the ballast itself finally fails completely, and several lamps have been destroyed for no good reason.
So, if the lamp is discolored on both ends, time for new lamps, if the lamp is discolored on one end, time to change both the lamps AND the ballast.