It IS possible for a bulb to start the arc, and yet not produce optimal lighting. However, this occurs very infrequently, and is therefore unlikely.
The most likely cause of poor light output (especially if there is no colour shift (bulbs are the same colour)) is that the focal point of the bulb is not aligned correctly with the headlight housing. First thing i'd do is check that the bulb is sitting flush with the mounting surface in the headlight.
Hot: 2001 Estoril M Roadster
ZCP 19's, ZHP knob, JL 8W3
Cold: 2002 TiAg M3 6mt
ZCP 19's supersports, ZHP knob, UUC short shift GROM, OEM 18's w310's,
http://absolutehid.ca hid kit