You could buy other Oakley Flak Jacket Sunglasses and swap out the interchangeable lenses to match changing weather or you could go from sunrise to sunset in these Flak Jackets with Transition Lenses. Transition Lenses feature photochromatic technology that automatically tints and adapts to varied light sources. These Flak Jacket lenses work best between bright to overcast light making them ideal for running backpacking trekking and climbing. Keep in mind that Transition eyewear cannot adapt quickly enough to changing light while driving or bike racing. Oakley's Flak Jacket represents a new generation of Oakley sport eyewear performance. The interchangeable lenses have a permanent hydrophobic lens that repels skin oil rain and sweat to optimize optical performance. The Transition lenses also resist smudges and clean easier than previous eyewear making the design better suited to endurance sports and extended climbing and backpacking. While some people found the Flak Jacket lenses easier to change than the Half Jackets it's all really a matter of getting used to changing lenses. Like learning anything new changing the lenses the first time around takes an extra moment or two. After that you can swap out lenses in a few moments and quickly adapt to new light conditions. Like the Oakley Half Jackets the Flak Jacket has a featherweight O Matter® frame with Unobtainium earsocks and the proven three-point fit. Unobtainium tends to grip more when wet so you don't have to worry about your Flak Jackets giving you the slip before you reach the finish line.