A wearable healthcare and lifestyle device acting as a personal assistant regarding the exposure to light (UV, light below and above 460 nm, infrared), physical activity, and sleep patterns of a user, and as a personal advisor in relationship with his lifestyle and noticeably his sleep and circadian rhythms.rnrnThe device named Lightmonitor could be used :rn- By researchers to investigate the influence of light (flux, duration, exposure) on: sleep and circadian disorders, seasonal or non-seasonal depression, metabolism disorders, memory troubles, physical activity disorders.rnrn- By researchers to assess photic strategies in the treatment of: troubles of sleep circadian rhythm, and sleep, for example in people having neurodegenerative pathologies or affective disorders.rnrn- By physicians as a diagnostic tool to assess a patient’s lifestyle in order to propose recommendations to improve sleep in shift workers or adolescents, improve sleep hygiene in the general population, increase physical activity,or prevent premature aging of the eye.rnrn- By physicians for monitoring patients in the course of light therapy treatments. They could assess whether adolescents, shift workers, patients have followed their recommendations to treat their circadian sleep disorder, or SAD, or insomnia.rnrn- By clinicians in applications wherein particular specific wavelengths of the light spectrum, have an impact on health. They could monitor the exposure to light of patients given photosensitizing medications or suffering from cancer, from age-related macular degeneration or other eye diseases.rnrn- By everyone as a mean to control systems in buildings or any other built environments in order to satisfy one’s health and comfort related requirements. The device would control blinds, lights, heaters, based on their activity, their biological clock,….