How did evenings (under Betsie’s direction) become the door to the wide world?

Father, Betsie, Corrie, Jop, Henk, Eusie, Leendart, Mary, Meta and Thea - enjoy a good quality of life, due to Betsie’s careful direction. In the evenings, they rig up a bicycle, which generates light from peddling, and Eusie gives Hebrew lessons, or they read Shakespeare aloud, or sing together.