During a typical night’s sleep, we spend about half of our time in what’s known as “light sleep,” or Stage 2 sleep. Despite its name, though, light sleep isn’t the lightest stage of sleep. To complicate matters further, when people refer to themselves as “light sleepers,” they’re not actually talking about this sleep stage.
Read on for more info about light sleep — both the stage and the characterization.
Where Stage 2 (NREM 2) sleep fits in
There are four distinct stages that we cycle through each night: Stage 1 (transition), Stage 2 (light), Stage 3 (slow-wave or deep sleep), and REM (rapid-eye movement). The first three stages are collectively known as NREM (non-REM sleep).
Even though Stage 2 is called “light,” the lightest phase of sleep is actually Stage 1, which is the short transition from the state of being awake to being asleep. “Stage 1 is light, it’s fragile, it’s tenuous,” says Michael Grandner, Ph.D., director of the Sleep and Health Research Program at the University of Arizona. “You’re supposed to be on your way; you’re not supposed to stay there, as opposed to Stage 2, where you are.”
We cycle through the stages over the course of the night (typically about four to five cycles). Overall, we spend about 5% of our sleep time in Stage 1 (transition), then roughly 50% in Stage 2 (light sleep), 20% in Stage 3 (slow-wave sleep), and 25% in REM sleep. However, these percentages can vary in people quite a bit based on a range of factors, including biological sex, medications, and more. For example, as we age, we naturally spend less time in Stage 3 sleep (slow-wave) and more time in Stage 2.
But even though we cycle through all of the stages of sleep multiple times each night, our Stage 2 sleep gets interspersed at various points. Stage 2 sleep is what we pass through before entering the deeper sleep that characterizes Stage 3. Sometimes we go from Stage 2 into Stage 3 sleep, but sometimes we then go back to Stage 2 sleep before entering REM sleep.
A better way to characterize Stage 2 sleep?
Dr. Seema Khosla, medical director of the North Dakota Center for Sleep in Fargo, describes Stage 2 sleep as the “runway” that prepares us for slow-wave or REM sleep. Our heart rate slows, our body temperature decreases, and our breathing becomes more regular during this stage.
Grandner prefers to call Stage 2 “regular” sleep rather than “light” sleep. “Light sleep is more of a technical term than a descriptive one,” he points out. So why is Stage 2 described as light sleep?
“When we think of light sleep, we think of something that’s shallow, not very restful, not very restorative. That doesn’t describe stage two at all.”
Stage 2 sleep is actually very restful and restorative, Grandner says.
An EEG recording during this stage will show single slow waves, known as K complexes, and bursts known as sleep spindles (which resemble spindles on a spinning wheel). These spindles are thought to help mask sound; this may be why we don’t wake ourselves up when we snore, Khosla says.
Additionally, sleep spindles play a role in memory consolidation and in mastery of motor skills.
What about light sleepers?
Those of us who consider ourselves light sleepers generally mean that we’re easily awakened — not that we’re spending too much time in Stage 2 sleep. A light sleeper likely has a different arousal threshold, Khosla explains, and may even be in a hyper-aroused vigilant stage (this can be common when you’re a new parent, so is sometimes informally referred to as “mommy ear”).
That said, though, waking at night is pretty normal. We wake most easily from Stage 1 (transition sleep): Hearing someone talking quietly, or some other slight noise, may be all it takes. This stage occurs not just when we’re drifting off to sleep for the night, but at various other points as well.
There may be specific reasons that we’re waking, such as having a partner who snores. “That can wake you up out of any stage,” Khosla says.
There may also be other factors, such as an underlying sleep disorder. “A lot of women with sleep apnea, for example, don’t necessarily snore or choke or gasp, but they have difficulty both initiating and maintaining sleep,” says Khosla. As a result, they may “feel like they’re just in very light sleep all night.”
Additionally, as we age, we’re also more likely to awaken during the night. This can be driven by a more frequent need to use the bathroom, but also because we spend less time in deep (Stage 3) sleep and more in Stage 1 and 2, which are easier to wake from.
The resulting sleep fragmentation may lead to thinking that you’re a light sleeper when, in fact, there are underlying factors.
If you find yourself waking frequently, it may be better to try to identify and address what’s rousing you from sleep — whether it’s an undiagnosed sleep disorder such as sleep apnea, or external factors such as temperature or noise.
It’s common to wake up briefly at night, Khosla notes. “It doesn’t always mean that there’s something wrong.”