According to the phase response curve, what effect does turning on the light in the middle of subjective night have?

Turning on the light in the middle of subjective night has the effect of delaying the circadian clock. This is based on the principles of the phase response curve (PRC), which outlines how various timing of light exposure can affect the circadian rhythms.

When light is introduced during the night, particularly when it is not expected, it disrupts the natural progression of the circadian cycle. Specifically, exposure to light during this time can shift the timing of the biological clock in a way that pushes the clock forward, thus delaying sleep onset and other rhythmic processes. In essence, it can cause the individual to feel alert when they should be winding down for sleep, extending their alertness phase.

This phenomenon is particularly relevant for understanding sleep disorders and managing schedules in professions that require work during traditionally sleeping hours. Melatonin production, which supports sleep, will be suppressed in this scenario, further indicating the delay in the circadian timing rather than advancement.