The short dark days of winter, related lack of energy, and low mood have always been part of life for those living in northern latitudes. For many, the gradual changes of the seasons are accompanied by the gradual degradation of their mental health. This disruptive effect is called Seasonal Affective Disorder (SAD). It is defined as major depressive episodes characterized by their seasonal recurrence for at least 2 consecutive years. Symptoms generally involve fatigue and a severe lack of energy leading to difficulty in performing daily activities as well as increased worry, anxiety, and irritability. Product Design in the field of SAD is positioned primarily in the treatment phase. Bright Light Therapy (BLT) products are used to attempt to alleviate the symptoms of the disorder. Efforts should focus on the prevention of mental illness to have a holistic impact on sustainable development. This project aims to identify an innovation opportunity where Product Design can be leveraged to prevent SAD. By leveraging semiotics, the study of signs and how meanings are created, in the field of lighting and design, a concept was developed that aims at complementing existing regulations in providing users with the conditions for improved well-being in the home. SAD is strongly linked to natural light and its cycles. Windows, the main provider of this kind of light in the home, have practical, comfort- and information-related roles. The developed concept aims at enhancing the meaning of windows to highlight our dependency on natural light cycles and prevent SAD. To effectively evaluate the concept and its effectiveness in creating meaning, it must be further developed and exposed to potential users.