An electrically-powered, patient-worn device designed be used by a layperson in the home (may additionally be used by a healthcare professional in a clinical setting) to emit red light for phototherapy primarily to treat musculoskeletal symptoms (e.g., arthritis pain, spasm, stiffness) and increase muscle relaxation through localized modification of cellular metabolism and/or improvement of blood circulation. It is in the form of a wearable thin adhesive hydrogel patch with integrated light-emitting diodes (LEDs) designed to be applied to the affected area. This is a reusable device.