Sleep Phase Disorders

Circadian Rhythm (Sleep Phase) Disorder

The term ‘sleep phase’ refers to the period of time spent asleep in a day. Although sleep varies from person to person, in general, most people have the sleep phase of about eight hours which occurs somewhere in the range between 9:00 pm and 8:00 am. 

Circadian rhythm sleep disorders are a family of sleep disorders affecting, among other things, the timing of sleep. A person’s sleep phase can cause them problems when it doesn't fit in their lifestyle and daily commitments. People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work, school, and social needs. They are generally able to get enough sleep if allowed to sleep and wake at the times dictated by their body clocks. Unless they also have another sleep disorder, their sleep is of normal quality.

Delayed sleep phase disorder and advanced sleep phase disorder are conditions of the body's timing system known as the biological clock or circadian rythm.

Delayed Sleep Phase Syndrome

model wearing light therapy device

A person with delayed sleep phase syndrome has trouble falling asleep before midnight, and sometimes won’t fall asleep until two or 3 o'clock in the morning. These people have a natural tendency to keep sleeping until 9 or 10 o'clock the next morning. This is not a problem if the sleeping times suit the individual’s lifestyle. It becomes a problem when the person tries to fall asleep at a ‘usual’ time but cannot. There may also be commitments in the morning such as school or work. For example, if a person with delayed sleep phase syndrome goes to bed at 10:00 pm, they may toss and turn for two or three hours becoming anxious and angry at their inability to fall asleep.  Sometimes the person will fall asleep for half an hour, and find they awake shortly after until 1 am or 2 am. The more the person is unable to sleep the more frustrated they become.

Delayed sleep phase syndrome can lead to varying degrees of sleep deprivation. If a person with delayed sleep phase syndrome has to get up between 6 am and 7 am to go to work and I only have 4 to 6 hours of sleep. This may leave them tired and cranky during the day. They may experience personal and/or social problems as a result of this tiredness.

It is common for delayed sleep phase syndrome to develop in early childhood or adolescence.

Advanced sleep phase syndrome

Advanced sleep phase syndrome is a condition (very similar to delayed sleep phase syndrome) in which patients feel very sleepy and go to bed early in the evening (e.g. 6:00–8:00 p.m.) and wake up very early in the morning (e.g. around 3:00 a.m.) and are unable to go back to sleep.


Once diagnosed, sleep phase disorders can be treated with bright light filtering in the mornings and bright light therapy in the evenings. The Feel Bright Light is a portable, at-home device uses the power of light therapy to reset the circadian rhythm.