HID bulbs last much longer than halogens on a normal life cycle. Hence, if one blows out, you should replace the other too given it likely won't have too much life left. The other reason for this is that HID bulbs fade in performance over time due to deterioration of the metal halide salts. Hence, even if you got a brand new 4300K bulb on one side while keeping an old 4300K bulb on the other, the color may be slightly mismatched simply due to varying bulb condition.LPSISRL wrote: I'll just had an extra set of bulbs. Not that I can really do anything with them as the color temps won't match...
It's a good practice to replace in pairs when the time comes.