Difference Between Dawn Simulation and Bright Light Therapy

Dawn and dusk simulation (DDS) therapy provides a departure from standard bright light therapy in the followings ways:

  • DDS therapy is used while in bed, during normal sleep hours. By contrast, bright light therapy is used during waking hours.
  • DDS therapy presents gradually changing light levels to mimic outdoor dawn and dusk transitions (when the sun is below the horizon). The maximum required light intensity is around 300 lux. By contrast, bright light therapy presents constant light at supra-sunrise levels (say, 10,000 lux).
  • DDS is a more practical, “automatic” treatment in that it hardly requires the user’s attention, and most of the signal is presented while the user is asleep. By contrast, bright light therapy requires scheduling waking hours for treatment.

Advantages of Dawn and Dusk Simulation Therapy

Although DDS therapy appears advantageous, there have been far fewer clinical trials using this method. Most tests have used a dawn signal alone, without the dusk signal, with overall results similar to that of bright light therapy: increased ease of awakening, with more alertness and energy, and an antidepressant effect. Case studies using a combination of dusk and dawn signals are very promising. The dusk twilight fade is scheduled around bedtime, and the dawn reaches its peak around wake-up time. People who have had difficulty falling asleep report smoother sleep onset in the presence of a dusk fade.

Effects of the First Dawn and Dusk Simulation Apparatus

The initial demonstration of DDS therapy in the late 1980’s was by Drs. Michael Terman and David Schlager at Columbia, using a complex mechanical device in which a precision motor rotated a set of vanes in front of a fluorescent light box, operating like a computer-controlled venetian blind. Although the mechanics were cumbersome, several important effects were noted:

  • The dim dawn signal served to cut short the body’s production of melatonin in the morning hours, which probably contributed to the increased ease of awakening.
  • After a week of daily home exposure to a naturalistic dawn set for early May (but delivered in midwinter), the circadian rhythm of melatonin production shifted to an earlier hour. Thus, the dawn simulation had a physiological effect similar to an eastward time zone transition.

The authors concluded that “twilight exposure appears able to promote circadian phase adjustments, morning melatonin suppression, regularized sleep patterns, and antidepressant responses. This represents the first indication in humans of physiological and/or behavioral sensitivity to such light signals.” Underscoring the logic of DDS vs. bright light therapy, the authors continued, “We hypothesize that non-modulated bright light constitutes a supernormal stimulus [that is, a stimulus with higher intensity than required under natural conditions]. The eyes may be primed at twilight hours for reception of changing intensities of low-level light.”

The Most Recent Dawn and Dusk Simulation Apparatus

The most recent DDS apparatus, suitable for home treatment, utilizes electronic controls and shielded incandescent/halogen lamps. Treatment strategies include choosing an optimum clock time for simulated sunrise or a desired calendar date. In one popular strategy, the user specifies the desired sleep length (for example, 7.5 hours), and the microprocessor “finds” a location on earth matching this nighttime duration at the summer solstice, and drives the lamps accordingly. In starting DDS therapy, users need to determine effective combinations of maximum light intensity, twilight duration and timing. Most prefer a sunrise of around 300 lux, but others require lower levels to forestall premature awakening. Far lower levels are often preferred for the dusk signal.

Several inexpensive “light alarm clocks” have been marketed, cloning the DDS concept, but with rapid dawn ramps (far faster than natural dawns) and restricted fields of illumination. These mass-market products have not yet received adequate clinical evaluation.

Further Information

Terman M, Terman JS. Controlled trial of naturalistic dawn simulation and negative air ionization for seasonal affective disorder. American Journal of Psychiatry. (2006) 163: 2126-2133.