2012 and 2013 Prius II in our household, and both have terrible illumination from the low beams. I regularly polish the plastic cover, makes little difference. Did the H9 upgrade on one, helped a little, did a LED upgrade on the other, no real improvement. However, the high beams on both are like photon torpedos in comparison, so I don't think there are issues with the headlight covers. I'm wondering if the round internal diffusers are a source of the problem? Can they be replaced or changed? Any other thoughts?