Try cleaning the inside of the rectangular bulb first.  Use a strip of
lint-free rag and alcohol.  Use a pencil with an eraser on the end to move
the cloth around inside. Make sure the bulb is dry before reinstalling.
Also, there are extra bright bulbs available too.  Got mine at Autozone.  Try
both cleaning and a bright bulb on one side and compare.  It was good enough
for me.  There has also been some talk about using relays and cleaning up the
grounds.  I haven't tried either, but check the archives if you are
interested.

Tom
'71 Westy, '85 Westy, '91 Carat, '81 VW Diesel Pickup