US Patent 10376207 Calculating a current circadian rhythm of a person

The invention relates to an apparatus (100) and a method for generating a model output x(ti) describing a circadian rhythm of a person (P) at a time ti. In a preferred embodiment, a light sensor providing the photic exposure (L(ti)) and an activity signal (A(ti)) indicating the current level of activity of the person (P) at the time ti based on motion measurements (via an accelerometer) are used to calculate a wakefulness variable (σ) that indicates if the person (P) is awake or sleeping. The wakefulness variable is then used to determine a driving term (N(t)) for a driven oscillator model (135) which simulates the model output x(t) under the joint influence of light and activity.