Your sleep efficiency for each night is calculated as a sum of the time you spent in both light and deep sleep divided by the total duration of the sleep session. Simply put, the more time you spent asleep, whether in deep or light, the higher percentage your efficiency will be.
% Efficiency = [(Hours Light Sleep + Hours Deep/REM Sleep) / Total Hours in Bed] x 100
% Efficiency = [(Hours Light Sleep + Hours Deep/REM Sleep) / Total Hours in Bed] x 100