Dawn

Sunrise

Sunrise is the instant at which the upper edge of the Sun appears above the horizon in the east. Sunrise should not be confused with dawn, which is the point at which the sky begins to lighten, some time before the sun itself appears, ending twilight...

 simulation is a technique originally developed to help treat seasonal affective disorder

Seasonal affective disorder

Seasonal affective disorder , also known as winter depression, winter blues, summer depression, summer blues, or seasonal depression, is a mood disorder in which people who have normal mental health throughout most of the year experience depressive symptoms in the winter or summer, spring or autumn...

, but can be used as a soundless alarm clock

Alarm clock

An alarm clock is a clock that is designed to make a loud sound at a specific time. The primary use of these clocks is to awaken people from their night's sleep or short naps; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but...

 to wake up the body naturally. Typically, the treatment involves timing lights in the bedroom to come on gradually, over a period of 30 minutes to 2 hours, before awakening.

History

The concept of dawn simulation was first patented in 1890 as "mechanical sunrise". Modern electronic units were patented in 1973. Variations and improvements seem to get patented every few years. Clinical trials were conducted by David Avery, MD, in the 1980s at Columbia University

Columbia University

Columbia University in the City of New York is a private, Ivy League university in Manhattan, New York City. Columbia is the oldest institution of higher learning in the state of New York, the fifth oldest in the United States, and one of the country's nine Colonial Colleges founded before the...

 following a long line of basic laboratory research that showed animals' circadian rhythms to be exquisitely sensitive to the dim, gradually rising dawn signal at the end of the night.

Clinical use

There are two types of dawn that have been used effectively in a clinical setting: a naturalistic dawn mimicking a springtime sunrise (but used in mid-winter when it is still dark outside), and a sigmoidal

Sigmoid function

Many natural processes, including those of complex system learning curves, exhibit a progression from small beginnings that accelerates and approaches a climax over time. When a detailed description is lacking, a sigmoid function is often used. A sigmoid curve is produced by a mathematical...

-shaped dawn (30 minutes to 2 hours). When used successfully, patients are able to sleep through the dawn and wake up easily at the simulated sunrise, after which the day's treatment is over. The theory behind dawn simulation is based on the fact that early morning light signals are much more effective at advancing the biological clock than are light signals given at other times of day (see Phase response curve

Phase response curve

A phase response curve illustrates the transient change in the cycle period of an oscillation induced by a perturbation as a function of the phase at which it is received...

).

Comparison with bright light therapy

Dawn simulation generally uses light sources that range in illuminance

Illuminance

In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of the intensity of the incident light, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per...

 from 100 to 300 lux

Lux

The lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface...

, while bright light boxes are usually in the 10,000-lux range. Approximately 19% of patients discontinue post-awakening bright light therapy due to inconvenience. Because the entire treatment is complete before awakening, dawn simulation may be a more convenient alternative to post-awakening bright light therapy. In terms of efficacy, some studies have shown dawn simulation to be more effective than standard bright light therapy while others have shown no difference or shown that bright light therapy is superior. Some patients with SAD use both dawn simulation and bright light therapy to provide maximum effect at the start of the day.

Other uses

In an elaboration of the method, patients have also been presented with a dim dusk

Sunset

Sunset or sundown is the daily disappearance of the Sun below the horizon in the west as a result of Earth's rotation.The time of sunset is defined in astronomy as the moment the trailing edge of the Sun's disk disappears below the horizon in the west...

 signal at bedtime, with indications that it eases sleep onset. In addition, the technique has been used clinically with patients who suffer from delayed sleep phase syndrome

Delayed sleep phase syndrome

Delayed sleep-phase syndrome , also known as delayed sleep-phase disorder or delayed sleep-phase type , is a circadian rhythm sleep disorder, a chronic disorder of the timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily rhythms, compared to the...

, helping them to awaken earlier in gradual steps, as the simulated dawn is moved earlier.

Non-clinical sleep and wake-up uses

A dawn simulator can be used as an alarm clock. Light enters through the eyelids triggering the body to begin its wake-up cycle, including the release of cortisol

Cortisol

Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...

, so that by the time the light is at full brightness, sleepers wake up on their own, without the need for an alarm.