Headlight bulbs

Has anyone else had problems with headlight bulbs blackening. Recently I noticed that my T80 lights had become dimmer than usual, when I looked at the head light bulb it had gone black, I fitted a replacement but in a few days it too had blackened. Voltage reg is working ok & rear light bulb is ok. Usually I have found that the headlight bulbs last a couple of years or so even though I use them all the time. It looks as though the last batch I bought (off eBay) may be sub standard Chinese made 'crap', so maybe it pays to buy a good quality brand. If these are available these days!