Photochromic sunglasses and goggles react automatically to the available sunlight making them excellent for many sporting activities. On overcast days the lens tints are medium to light. On sunny days they darken to a comfortable sunglass tint and when you go inside, they lighten up. Since they darken and lighten in response to the amount of sunlight you can wear them from dawn to dusk and never have to take them off. Clear to smoke lenses are best for general purpose use. Yellow to smoke lenses are particularly good for changeable weather, at their lightest (yellow) they are perfect for overcast conditions and they darken to a darker tint. Also known as photochromatic, transitional, day to night or reactolite sunglasses they're available in a variety of lens and frame options.
Please note, photochromic lenses react to UV rays and will not darken when worn behind a helmet visor or motor vehicle windscreen that filters out UV light. They must be exposed to direct sunlight to darken.