I just bought a pair of 23 Watt from Wal-Greens (100 Watt equivalent house brand $3.99) and I am experiencing the ring in the tube problem (I only thought the T-12s had this problem) Only one of the two lamps experiences this problem (Both bulbs in different fixtures but on the same circuit) After a while it will go away but the ends of the tubes are already noticeably blackened (Like when they are ready to burn out) I know I probably have a defective lamp, and I will not worry about that I am just mostly wondering what causes this? I have never seen it in a CFL lamp before only the linear T12 4-8' lamps Thanks I really am interested just to know the problem or what causes this ring in the tube

Thanks