Synonyms for Lightsomeness (same or very similar meaning)
WordNet sense 1 (the cheerful feeling you have when nothing is troubling you):
insouciance, lightheartedness, carefreenessWordNet sense 2 (the gracefulness of a person or animal that is quick and nimble):
agility, legerity, lightness, nimblenessFrom the ODE community, based on WordNetadd/edit