To clean a roof lantern,  needs to start by dusting off loose dirt, leaves   and cobwebs with a softer brush. Then, washing the glass and frame with a mild, purified water  solution and a non-abrasive sponge or cloth. Rinsed thoroughly with clean water and dried with a squeegee  to prevent streaks and water spots. Always best done  on an overcast day to prevent the cleaning  from drying too quickly. Annual roof lantern cleans can work on some houses but if near to trees may need attention more often