Brown lenses block more blue light thus reducing haze and glare and are more popular in Europe. Gray lenses tend to be more popular in the US and are a good choice for bright conditions.The only difference between the two lenses is personal preference..

Sure,you can.You can wear them at any place for any activity, especially outdoor activities because they are 100% UV protected. They are also available in impact resistant lenses which are also very light and thin.