Sleep is a reversible state during which you're not aware of anything and you don't respond to your environment.
We tend to sleep about 6-9 hours a night during which we experience several sleep cycles, each lasting between 1.5 and 2 hours. Each cycle progresses through a series of sleep stages beginning with NREM (non rapid eye movement) sleep (stages 1 - 4) and moving through to REM (rapid eye movement) sleep, which is associated with dreaming. NREM sleep makes up 75 - 80% of total sleep with a high proportion of stage 3 and 4 sleep (slow wave or deep sleep) at the start of the night. The amount of REM sleep in each cycle increases across the night.
The quality, timing and length of sleep are dependent upon an interaction between two biological systems in our brain. Firstly, there is a body clock which drives daily 24 hour rhythms in our body functioning and also in our behaviour including our sleep/wake patterns. These daily rhythms are known as circadian rhythms. Secondly, there is a 'sleep monitor' (called the sleep homeostat) which essentially acts like an egg timer in our brain and tracks how long we are awake by a build up of sleep pressure (sand filling up the egg timer). The longer we are awake the greater the sleep pressure (fuller timer) and when we go to sleep this pressure disappears (timer turns over and empties) ready to begin again when we awake. Particular groups of cells in the brain, and the substances they produce, are involved in maintaining a wake state whilst other groups of cells can produce substances to oppose this and induce sleep.
Problems with sleep
Disruptions to sleep are widespread and highly variable, and can be the result of disruptions to either the body clock and/or the 'sleep monitor'. One well known cause of sleep disturbances is when the body clock is not correctly co-ordinated with local time, such as occurs in jet lag after flying across time zones or during shift work. Depending on the situation it can be a struggle to fall asleep (sleep onset insomnia) or to stay asleep (sleep maintenance insomnia) such that the individual may only sleep a very short time at night and will suffer from fatigue and sleepiness during the daytime.
The body clock not being co-ordinated with local time is a much more common occurrence than is often realised. Simply going to bed and getting up later at the weekends can allow the body clock to drift later in time and make it difficult to wake up on a Monday morning to go to work. Individuals who are extreme morning types (larks) and extreme evening types (owls) can really struggle when trying to operate in a 9 - 5 society. Larks, who go to bed and wake up very early, may feel tired at work/college if they have been awake for several hours by the time they get there, and may not be able to socialise in the evenings as they are tired and want to go to bed. Owls will struggle to get up in time for work/college and as they may not have had enough sleep they may not perform well and will become increasingly fatigued.
Certain ages are associated with particular sleep problems; teenagers tend to have later sleep patterns and struggle to get up in the morning for school. These delays in bedtimes and wake times seem to be due to actual biological changes in the body clock or 'sleep monitor' rather than just being lazy! As we get older, there is an increase in the number of sleep problems experienced and these include waking up early, increased awakenings at night and trouble staying asleep. Again, these could be due to changes in the body clock or the 'sleep monitor' but it has also been suggested that they could be due to the light environment. Older people tend to spend more time indoors due to reduced motility and not going to work, resulting in them being exposed to less outdoor bright light. Furthermore, as we get older there are changes in our eyes which can reduce the amount of light, particularly blue light to which the body clock is most responsive, reaching the light sensitive receptors at the back of the eye. As light is essential for keeping our body clock co-ordinated to the 24 hour day, this reduction in light being transmitted to the brain could disrupt the synchronisation of the body clock to local time and also reduce the strength of the signals given by the body clock to regulate sleep patterns.
Finally, a problem that is experienced by many people is the inability to feel alert and perform when we first awake and this is known as sleep inertia. It is worst if you are awoken from sleep ~ 2 hours before your normal wake time as this is the sleepiest internal time, the lowest point in your body temperature rhythm. The stage of sleep that you are woken from will also affect how severe the inertia is, being worst if you are woken from NREM deep sleep (stages 3 and 4) rather than REM.
How can light therapy help?
Light is able to synchronise the body clock to the 24 hour day and reset the timing of the body clock to adapt to being on a new light/dark (wake/sleep) cycle, for example after flying to a new time zone. These effects of light can be very beneficial to sleep patterns. The resetting effect of light depends on the time of day that it is administered and so, if you are travelling to a new time zone you can calculate the most effective time of day to use your light box based on your sleep schedule at home and your destination time zone. Light at the correct time will hasten your body's adaptation to local time whereas light at the wrong time can actually push your body clock in the wrong direction and prolong jet lag.
For the majority of people the body clock runs at slightly longer than 24 hours and so requires a morning light cue to remain synchronised to local time and ensure good quality sleep at the desired time. In the dark winter mornings when this cue is absent it may be beneficial to supplement your clock by using a bright light box upon awakening to keep your body clock on track and your sleep patterns consistent. Morning bright light could also be beneficial for people who need to push their sleep times earlier such as extreme late types (owls), teenagers and for commuters who need to wake up early. Extreme early types (larks) who want to push their sleep patterns later in time could use light boxes in the early evening to achieve this effect.
Older people can use bright lights in the morning and early evening to provide strong dawn/dusk cues to their body clock which should not only maintain the clock on local time but also boost the strength of the signals from the clock. Together this should result in good quality, consolidated sleep at the desired time.
The symptoms of sleep inertia upon awakening, that make it difficult to get out of bed in the morning, may be alleviated by using a dawn simulator. Studies have shown wake-up lights like the Lumie Bodyclock range that gradually turn on and get brighter during the last 30 min of sleep can reduce complaints of sleep inertia.
Bright light has been shown to immediately increase levels of alertness, boost mood and improve performance. Thus, if you are feeling sleepy during the daytime because of not being able to sleep well at night for whatever reason then having a light box at your desk at work could directly help to improve the way you are feeling.
Light therapy for better sleep
1. I struggle to get to sleep
Difficulties in falling asleep at the time you want could indicate that your body clock is set at a later time than desired for your schedule. You could use morning light to help reset and maintain your clock at an earlier time. Sitting in front of a bright light box upon awakening, for example while having breakfast, will push your body clock earlier in time and make it easier to fall asleep. A dawn simulator like Bodyclock, with a gradually increasing light signal during the last 30 min of sleep, could also be beneficial in resetting your clock and waking you up.
2. I oversleep in the morning
Oversleeping in the morning could again indicate that your body clock is set at a later time than desired or that you experience extreme sleep inertia upon awakening which makes it difficult to get up. Utilising a Bodyclock, where light steadily increases to a maximum during the last 30 min of sleep, could help to reduce the symptoms of sleep inertia and gradually wake you up as well as acting on your body clock.
3. I have no problem getting to sleep but have interrupted sleep/wake up much too early
Waking up too early could suggest that your body clock is set an earlier time than is suitable for your schedule. It is possible to push your body clock later in time by using a bright light box for 30 min in the early evening finishing at least 1 hour before you want to go to bed.
4. I sleep well, but my job demands I wake earlier than I naturally would
If you need to wake up earlier than usual then you can use a bright light box in the morning for at least 30 min upon awakening to shift your body clock to an earlier time. Alternatively, you could use one of the Bodyclock wake-up lights, where light gradually increases to a maximum during the last 30 min of sleep, to reduce sleep inertia (grogginess and inability to perform tasks upon awakening), which would be exacerbated by waking too early, and shift your body clock.
5. I fall asleep at different times of the day, I can't establish a regular sleep pattern
An unstable sleep pattern could indicate either that your body clock is receiving weak light signals from the environment (e.g. during winter months) and is therefore not stably co-ordinated with local time or that your body clock is only providing weak signals to your body so sleep is not consistent. Using a bright light box in the morning upon awakening and again in the early evening will provide strong dawn and dusk cues to your body clock which will help to fix it appropriately to local time. In addition, using a bright light box during the daytime at work will provide further cues to your clock to distinguish day from night and increase the strength of the signals from your clock to the body, hopefully stabilising sleep.
6. I work shifts
Fully adapting to a rapidly changing shift schedule (e.g. 2 early mornings, 2 late afternoons/evenings and 2 nights) is not possible due to the fact that your body clock does not instantly reset to a new light/dark cycle. In such situations sleep may be very disrupted or shortened due to having to get up earlier than usual or due to not being able to sleep for long during the daytime following a night shift as the clock is not adapted. Thus, if your work pattern is rapidly changing it may be beneficial to use a bright light box upon awakening or a Bodyclock, regardless of the current shift, to boost alertness levels and minimise sleep inertia upon awakening. If the shift schedule changes more slowly then it may be possible to use light to adapt to each shifted sleep pattern. To adapt to working early shifts you would need morning bright light; to shift yourself to working late evening shifts you would use evening light to push your body clock later. The timing of the light and the sleep schedule could be pushed later in time again to help you adapt to working overnight.
In addition, when working night shifts it may be difficult to remain alert and perform well during the night, particularly towards the end of the shift (4-6am), which could have consequences for safety and efficiency. If it is possible to use a bright light box while at work, e.g. next to a computer, in lounges during coffee breaks, this could help to maintain alertness and also help to push the body clock later in time and adapt to sleeping during the daytime. However, bright light boxes during any work shift will help to boost alertness and performance which will always be beneficial. It should be noted that bright light exposures do not need to be continuous to have a positive effect. Frequent short bursts of light can be very beneficial for maintaining alertness and performance, and also for shifting the clock.
Difficulties in falling asleep at the time you want could indicate that your body clock is set at a later time than desired for your schedule. You could use morning light to help reset and maintain your clock at an earlier time. Sitting in front of a bright light box upon awakening, for example while having breakfast, will push your body clock earlier in time and make it easier to fall asleep. One of our Bodyclock dawn simulators, with a gradually increasing light signal during the last 30 min of sleep, could also be beneficial in resetting your clock and waking you up.