Sleep efficiency is simply the total sleep time to time in bed expressed as a percentage. With a score over 80% as good sleep efficiency. For example, if a person spends 8 hours in bed (from 10 p.m. to 6 a.m), at least 6.4 hours or more should be spent sleeping to achieve an 80% or greater sleep efficiency. Most healthy and young adults have sleep efficiencies above 90%.
Sleep efficiency is often used as a score in insomnia research and helping people with insomnia as it shows the core problem insomniacs have – time in bed awake and not sleeping.
It is worth noting what is being measured as time in bed… as many people may be in bed but not actively trying to sleep and if that’s included in the measurement then it will lower the sleep efficiency score (1). It is also worth noting that a score of 100% doesn’t indicate perfect sleep efficiency rather it can indicate someone who is exhausted!
Sleep latency refers to the amount of time it takes a person to fall to sleep. For example, if a person goes to bed at 10:00 and falls to sleep at 10:15, the sleep latency is 15 minutes. Normal sleep latency is 5-15 minutes. Sleep latency less than five minutes may suggest some degree of excessive sleepiness. Sleep latency greater than 15 minutes may suggest some difficulty with falling asleep (sleep initiation).
Reference:
- Reed DL, Sacco WP. Measuring Sleep Efficiency: What Should the Denominator Be? J Clin Sleep Med. 2016 Feb;12(2):263-6.