What is Sleep Latency?

Good sleep latency means falling asleep not too long after bedtime.
Good sleep latency means falling asleep not too long after bedtime. Tetra Images/Getty Images

Sleep latency, also known as sleep onset latency or SOL, is the amount of time it takes to fall asleep after the lights have been turned off. Ideally, it should take a brief amount of time to fall asleep after the lights have been turned off, but not too long.

The time is takes one to fall asleep after the lights are turned off related directly to an individual’s sleep efficiency and sleep debt. An ideal sleep latency also lays the foundation for a solid night's sleep.

Sleep Latency's Relation to Sleep Efficiency

Sleep latency is related directly to sleep efficiency. If an individual spends the majority of the time that they are in bed in an evening actually asleep, than they are considered to be sleep efficient. However, if an individual spends a lot of the time that they are in bed not actually asleep, but trying to sleep, than that is not considered to be sleep efficient.

A sleep efficiency of 85% is considered to be normal, while a sleep efficiency anywhere above 90% is considered to be very good. A sleep efficiency lower than 85% is considered to be poor. Sleep latency relates directly to sleep efficiency, because if a person is able to fall asleep quickly, they are more likely to have an efficient sleep. If a person has ideal sleep latency, they are likely to have good sleep efficiency as well, as the two go hand in hand.

Sleep Latency and the Sleep Cycle

An ideal sleep latency lays the foundation for a solid night's sleep, which occurs in two basic states throughout the night.

The two stages of sleep that occur throughout the night are rapid eye movement sleep (REM) and non rapid eye movement sleep (NREM). REM sleep is a deeper form of sleep than NREM sleep, however both states of sleep are directly impacted by sleep latency. If an individual has good sleep latency and is able to fall asleep within a reasonable amount of time, they will have a better chance of progressing through the stages of sleep comfortably and in turn enjoy a deep sleep.

Sleep Debt's Impact on Sleep Latency

Sleep latency also relates directly to sleep debt, which is the overall effect of not getting enough sleep. Sleep dept can accumulate over time, and in turn lead to mental and physical fatigue.

Sleep debt has a direct impact on sleep latency, as those who are extremely tired, or have a lot of sleep debt, will likely fall asleep quicker than someone who is better rested and does not have any sleep debt. There are many factors that determine that an individual's sleep latency, and their overall sleep debt debt is a big one. Falling asleep almost immediately upon laying down is often a sign of sleep debt, and thus a sign that you should try to get more sleep on a nightly basis.

Examples: My sleep latency is typically normal, although I was very tired last night and I fell asleep in about five minutes.

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