Final answer:
Before electric lighting was widely available, adults averaged approximately 7-9 hours of sleep per night. With the advent of electric lighting, people started sleeping less and averaged fewer than 7 hours of sleep per day by the time they reached 65 years old.
Step-by-step explanation:
The average amount of sleep for adults before electric lighting was widely available was approximately 7-9 hours per night. According to the National Sleep Foundation, newborns require the most sleep (between 12 and 18 hours a night) and this amount gradually declines as we become adults. With the advent of electric lighting, people became more active during nighttime hours and started sleeping less, averaging fewer than 7 hours of sleep per day by the time they reached 65 years old.