A system configured to estimate a circadian phase of a subject , the system comprising: a sensor configured to detect a motion of the subject and adapted to generate output signals conveying information related to an activity level of the subject based on said motion; and one or more physical processors , characterized in that the one or more physical processors are configured to: determine a set of activity parameters related to the activity level of the subject, wherein the set of activity parameters is based on the generated output signals; generate a set of estimated light exposure parameters based on the set of activity parameters using the equation: LE t = 1 / K ⋅ activity t γ − c 0 , 1 < γ < 3 , wherein LE(t) is an estimated light exposure parameter, activity(t) is an activity parameter and K, γ and c 0 are constants; and estimate the circadian phase of the subject based on the set of estimated light exposure parameters, wherein estimation of the circadian phase is based on a model including a set of light exposure parameters, wherein the model is a pacemaker oscillator model, wherein the pacemaker oscillator model is described by a second-order differential equation: d 2 / dt 2 x t − μ ⋅ 1 − 4 x 2 d/dt x t + 2 π / τ 2 x t = d/dt B t + N t , wherein x(t) is a dependent variable that is assumed to vary analogously with the subject's core body temperature, μ is a stiffness factor, τ is an intrinsic period, B(t) is a photic driving term and N is a non-photic driving term, wherein the photic driving term B(t) includes the set of light exposure parameters, and wherein estimation of the circadian phase includes a substitution of the set of light exposure parameters included in the model with the generated set of estimated light exposure parameters. a sensor configured to detect a motion of the subject and adapted to generate output signals conveying information related to an activity level of the subject based on said motion; and one or more physical processors , characterized in that the one or more physical processors are configured to: determine a set of activity parameters related to the activity level of the subject, wherein the set of activity parameters is based on the generated output signals; generate a set of estimated light exposure parameters based on the set of activity parameters using the equation: LE t = 1 / K ⋅ activity t γ − c 0 , 1 < γ < 3 , wherein LE(t) is an estimated light exposure parameter, activity(t) is an activity parameter and K, γ and c 0 are constants; and determine a set of activity parameters related to the activity level of the subject, wherein the set of activity parameters is based on the generated output signals; generate a set of estimated light exposure parameters based on the set of activity parameters using the equation: LE t = 1 / K ⋅ activity t γ − c 0 , 1 < γ < 3 , wherein LE(t) is an estimated light exposure parameter, activity(t) is an activity parameter and K, γ and c 0 are constants; and estimate the circadian phase of the subject based on the set of estimated light exposure parameters, wherein estimation of the circadian phase is based on a model including a set of light exposure parameters, wherein the model is a pacemaker oscillator model, wherein the pacemaker oscillator model is described by a second-order differential equation: d 2 / dt 2 x t − μ ⋅ 1 − 4 x 2 d/dt x t + 2 π / τ 2 x t = d/dt B t + N t , wherein x(t) is a dependent variable that is assumed to vary analogously with the subject's core body temperature, μ is a stiffness factor, τ is an intrinsic period, B(t) is a photic driving term and N is a non-photic driving term, wherein the photic driving term B(t) includes the set of light exposure parameters, and wherein estimation of the circadian phase includes a substitution of the set of light exposure parameters included in the model with the generated set of estimated light exposure parameters. <EOS>