Both of the low beams on my 98 S70 failed in the last month (one was
5 years old and the other 4 -- a record for a 98 S70, I'm sure). In
any case, the parts stores were all out of the correct bulbs; so, I
swapped the bulbs with my high beam bulbs (in the S70 it is the exact same
bulb, high beams just aim higher). I was surprised at how brigter the
light was. I guess the light output drops over time or maybe the bulb
glass fogs (anyone know?). New bulbs might be all you need.

Note if you change bulbs, don't touch the glass with your skin (the oil
on your hands will cut the bulbs life) and wear eye protection since they
are sealed and pressurized and can pop if dropped (thats the warning on
the bulb packaging).