The dark lens is used for normal daytime lighting.
The clear lens is used for low daytime light or night time conditions
The amber lens is for seeing in harsh light conditions such as haze or reflected snow.
The gradient lens is used for bright outside light conditions and dim light cockpit conditions so that you can see the instruments.
The High Contrast visor (HCV) provides the wearer with a heightened and enhanced field of vision when flying in low light conditions.