Eye protection is vital for most outdoor activities. Glasses will keep wind, insects, rain, spray and dust out of your eyes. Dark ones will cut down on light so you don't have to squint to see where you're going. All glasses should eliminate harmful UV rays, protecting your retinas from damage. So that you can protect your eyes in all conditions, glasses with interchangeable lenses are useful. Either that, or get yourself one pair for bright, dull and dark.