A reader asks:

In dawn/dusk simulation therapy, how important is the dusk simulation part? Also, can dusk simulation be successful even if used at different times in the evening?


Formal clinical trials have concentrated on dawn simulation, without the dusk simulation. Dawn is effective on its own. Clinical case studies suggest, however, that addition of the dusk signal at bedtime can be very helpful for people who have trouble falling asleep. Subjectively, it has a soporific quality, not unlike the sensation one gets when taking a low-dose, short-acting sleeping pill. When the dusk signal was added, some patients immediately fell asleep up to two hours earlier than usual. There are no studies or cases to report that used dusk simulation on its own, without the dawn signal. Possibly this would be useful as a soporific for people, with insomnia at bedtime, who have no problem with spontaneous rising in the morning. As for optimum timing of the dusk signal, case studies suggest that beginning the fade 20 minutes before desired sleep onset is effective. Of course, you have to be in bed to observe the fading light. . . .