The ID2 basic filter is a LST Bright, which creates a brightening effect while still offering high light absorption. This makes it absolutely ideal to be used in foggy conditions & hazy light. If the sun suddenly blazes down on the mountain or trail, a darker filter needs to come out. With just two clicks, you can quickly attach the second LST active silver filter to the front part & place it on top of the basic filter from outside. Also, the ID2 Pro is a helmet-compatible goggle using a unique 2-frame levelling system.