Another idea I just tried and like very much --
Go to Walmart or auto parts place, and get some 5% or 20% VLT CLING window tint (about $3.00 for the 5" wide role)
Cut a 2" by 12" strip, round the edges -- soap wet the outside of your clear shield, position at the top (will slide around to let you position it)-- smooth on and squeegie out the water.
I put 20% on some, and like the 5% better -- it's just a 'visor' strip, doesn't come off unless you peel it off -- so you have the bottom half clear (easier to see gauges, GPS, radar, etc) Works good in all lighting conditions.
Another cheap trick -- Walmart has auto detailing 'polishing' cloths -- which are very soft thin cotton and 2 layers sewn together (i think about $5 for a roll of 5 or 6 of them.) Cut a slit in the side, and you can stick in your spare/tint shield -- makes a very nice visor bag.