„0” category    lets 80-100% of the light through and is designed to be used on cloudy days.

 „1” category    lets 43-80% of the light through and is designed to be used on days with little sunshine.

 „2” category    lets 18-43% of the light through and is designed to be used on quite sunny days.

 „3” category    lets 8-18% of the light through and is designed to be used on very sunny days.